Please visit our Sponsors

FAQs about Dissolved Oxygen in Captive Aquatic Systems

Related Articles: Dissolved Oxygen and Aquariums,

Related FAQs:  Carbon Dioxide

All macro-life in the seas requires oxygen.

Japanese Dragon Eel HELP!!!!!! Mysterious losses... env.      4/6/17
I was wondering if you guys could possibly shed some light on a problem I'm having with Japanese Dragon eels.
<I will respond here and have sent your message on to MarcoL for his sep. resp.>
I am currently on my 3rd specimen within a 2 year period. The other 2 passed away after being in my current tank after 1 year and about 7 months respectively. Unfortunately, the one in my tank now I fear won't make it
through the night, and has only been in the tank for 1 week.
<Mmm; something wrong here... environmentally likely. Do you measure dissolved oxygen?>
I have a 150 gallon display tank with a 20 gallon sump setup and refugium. I run a protein skimmer, carbon reactor, and biopellet reactor.
<Why this last?>

Temp 78F, ph8.2, salinity 1.023-1.025, ammonia 0, nitrite 0, nitrate 20-40.
There is about 130 pounds of live rock, sand bottom, and terracotta pots (non glazed) in the main tank. There are also anywhere from 6-12 damsels in the tank at any given time, who do not seem to ever be affected (3 of which have been in the tank since the beginning).
<A good clue>

Diet consists of haddock, striped bass, squid, silversides, shrimp, krill, etc... Every eel has appeared to be in great health. Very active during the day. Very social with anyone that walks up to the tank. Great appetites. However, out of the blue it is like a switch is flipped and they stop eating, begin "gasping",
<This too>

become very lethargic, then die within a day or two. I have tried water changes, antibiotics, antiparasitics, without any luck. The first 2 eels were around 18-24 inches, while this new one is only about 12 inches. Any ideas what could be going on and why it only affects the eels?
<The DO issue comes to mind most prominently. A 150 isn't much room for a large eel... I'd add aeration... mechanically; and check to see that O2 is near saturation (7 or so ppm) here. Bob Fenner>
Thanks for any advice or help, Evan
Fwd: Japanese Dragon Eel HELP!!!!!!     4/6/17
I forgot to mention I have a full cleanup crew of Nassarius snails, blue legged hermits and peppermint shrimp that also appear to never be affected.
<Also leading me to suspect gas solubility issue.
Re: Japanese Dragon Eel HELP!!!!!!     4/6/17

Thank you for such a quick response...sadly though, this eel has passed as well. In terms of O2, how do I measure it?
<There are colorimetric assays like for much of what interests aquarists water-quality wise; as well as more expensive electronic meters>
Would the protein skimmer add enough O2 into the system?
<Not necessarily, no>
Could the terra-cotta be leaching some sort of poison?
<Mmm; good question: A point of fact is that there ARE other possible sources of morbidity, mortality here that would disfavor a large Muraenid (over damsels, the mix of invertebrates you mentioned)... I would remove
ALL that is questionable. I might avail myself of PolyFilter... as an aid (via coloring) as to what might be trouble here>
If O2 related, why do you think the larger eels lasted so much longer than the little one, who only survived 1 week and was doing great at my LFS for months in a much smaller tank and a Kidako eel tankmate?
<Can't say directly... but this IS the case... that smaller eels are more easily poisoned, die from env. stress vs. larger. I would have you (it will take a while) read generally re such HERE:
AND the linked files above. Bob Fenner>
Re: Japanese Dragon Eel HELP!!!!!! Plus DO f'      4/7/17

Thanks again for your insight. What is the best method in order to add more dissolved O2 to the system?
<Mmm; lower temperature, more circulation, total turnover (w/ all water skimming the air/water interface); pump, power-head discharges set near the surface, mechanical bubblers... Biotowers...
I added two more power heads to aerate the water in my sump. They make a lot of bubbles, of which rise to the surface and dissipate...is this actually doing what is needed?
<A help; yes. B>

Oxygen: The experimenting SW aquarist    3/19/11
I've been in the saltwater hobby for over ten years now and have gotten pretty good at keeping the basic parameters such as temp, spg, Alk, and pH consistent.
So now I want to explore a little bit deeper and learn about oxygen...or really oxygen levels.
Is it as simple as just buying an oxygen test kit and testing for it?
<Yes, insofar as oxygen test kits tell you anything. Do please bear in mind that oceanographers use oxygen testing devices and protocols that are difficult and expensive, and the equivalent test kits sold to aquarists are very much "ball park" estimates. Furthermore, oceanographers will do a series of test across a 24-hour period, because oxygen concentration varies dramatically through the day/night cycle, especially in enclosed bodies of water like tide pools and lagoons.>
Does it make sense to test for both oxygen and dissolved oxygen?
<Dissolved oxygen is the only stuff that matters, and that's what your test kit will measure. All the animals, plants, algae and other organisms in your aquarium depend upon dissolved oxygen unless they're able to use air as well -- not a common trait among reef organisms, but quite common among intertidal ones. And even air-breathers, including ourselves, are dependent on how much oxygen dissolves into the wet layer that coats the inside of our lungs -- contrary to popular misconception, the blood does not absorb oxygen from the air, but from the oxygen-rich mucous inside the lungs.>
I think it might be fun to find out how much oxygen is in the tank and then play around with the return line (from the canister filter) to see if I can increase oxygen via surface agitation and in turn raise the pH.
<Canister filters remove oxygen from the water, that much is certain. But they also produce strong outgoing currents of water that help circulate water from the bottom of the tank (where dissolved oxygen will normally be at lowest concentration) up to the surface (where dissolved oxygen will be at its highest concentration). Agitating the surface of the tank may increase the overall surface area of the water/air interface, but this is probably not a limiting factor in most aquaria. What causes problems in aquaria is insufficient movement of water from the surface, where it oxygen from the air diffuses into the water, down to the bottom. Powerheads and airstones do most of their good work in this regard, by "turning over" the
water, keeping the bottom layer moving upwards. In the wild, wind, waves, and especially upwelling currents have the same effect. Temperature is a much-overlooked issue as well. As temperature goes up, the solubility of gases including oxygen goes down, often dramatically. That's why a warm bottle of soda loses its fizz so much faster that one that's ice-cold. At the same time, as temperature goes up, the metabolism and therefore oxygen requirements of organisms goes up. Marine aquaria are frequently given to being kept much warmer than would be normal in the wild, with the net result that overheating by the lights especially causes oxygen concentration to drop at the same time as the organisms start demanding
more oxygen to keep pace with their faster metabolism! In many marine tanks, installing a chiller or otherwise reducing high temperatures would be a good way to optimise oxygen concentration and ensure long-term success with organisms unable to adapt to higher than normal temperatures. In fact this is a major source of mortality in coldwater systems -- coldwater marine organisms can easily suffocate at the low oxygen concentration present in even luke-warm seawater.>
Any advice or opinions would be greatly appreciated.
Thank you,
<Cheers, Neale.>

Re: Oxygen (RMF, feel free to chip in)-- 03/20/11
Wow! A lot more thorough than what I was expecting but I should have known as this site has always been a source of high quality info. Thank you Neale.
<No problem.>
Got two more for you.
If it's not too complicated and understandable by the average person (or even understood at all), could you please explain how oxygen is removed by canister filters? Because It doesn't seem to make sense since a canister filter is completely sealed. I see no way that air could escape. It must be somehow turning the oxygen into something else. Am I close?
<Yes. Canister filters -- at least when performing biological filtration, which they almost all do after running for a few days -- contain aerobic bacteria that need oxygen. They extract oxygen from the water pumped into them. So the water going out of the canister will, by definition, contain less oxygen that the water that went into them. Contrast this with a wet-dry filter for example, where water and air mix inside the filter, allowing oxygen from the air to top up the oxygen concentration in the water. Wet-dry filters therefore don't tend to lower oxygen concentration, despite being biologically active.>
And is there another type of filtration that can be used remotely, like a canister filter, that doesn't remove air from the water?
<Yes, any filter that mixes air with the water as it enters the filtration chamber. Most sumps, wet-dry filters, bio-ball filters, hang-on-the-back filters and others work this way. These filters will either lower oxygen concentration only slightly, or not at all, or maybe even raise it, depending on how biologically active they are and how well oxygen diffuses into the water while the air and water mix. Filters that extract oxygen from the water include internal canisters, external canisters, sponge filters, and undergravel filters. Live rock will also extract oxygen from the water, as will a DSB. Such filters will tend to lower oxygen concentration in the water.>
Thanks again,
<Cheers, Neale.>

Creating Experimental Scenarios, oxygen conc.  1/13/11
Hello Crew, and thank you again for a seemingly unlimited supply of reading material. I write to you today not with my usual ID questions, but one of hypotheticals.
I am doing some research into gene expression, and I plan to set up a series of experimental invertebrate tanks to attempt to control several odd variables. I say odd because both are conditions that aquarists strive to avoid; I need to generate both hypoxic and hyperoxic conditions for extended periods, within the tolerances of the organism, of course. I am in the early planning stages, and while I haven't been mulling it over too long, I am at a loss to think of safe and controlled methods to simulate these environments.
<Hypoxic... cover the water surface area... meter DO; Hyperoxic, "bubble in O2" measure/meter>
I can really only think of depletion and displacement for hypoxic, and supplementing oxygen for the hyperoxic, but none seem safe or consistent.
<Oh, can be w/ gear>
I figured that consulting a bunch of skilled aquarists might be my best bet for finding either another study done or some more ideas on how to generate my oddball conditions. I appreciate any guidance you can give. Again, thank you.
<Welcome. Bob Fenner>

Eel <comp.> and Dissolved Oxygen Problems. - 8/8/8 Hi Crew, <Hello Adam.> Let me thank you in advance for the great site and your help with my concerns. I have scoured over your FAQs but haven't found the answers to my question. I'm a relative newbie to the marine aquarium hobby and have certainly made more than my fair share of mistakes thus far. I cycled my tank for six weeks with live rock and have had fish in there for a little more than five weeks. So my tank is almost three months old. I have had two weeks of hell with my aquarium. I have resolved most issues so I will not waste your time going over everything that has happened. I have two main concerns I need help with, but will go over the basics first. Set-up: 100 gallon FOWLR tank 2 Emperor 400 Filters 65 lbs of live rock 100lbs of sand Inhabitants: 2ft zebra moray eel 10in snowflake eel 1 1/4in dwarf lionfish <Might become prey to the snowflake, when it gets older.> 1 1/4in fu man chu lionfish 3/4in sphex lionfish 1in flame angel 2in starry-eyed puffer <Arothron stellatus? Not recommended for any tank smaller than 1000 (one thousand) gallons. This fish can reach 30 inches for sure and was even reported at almost 50 inches in nature.> 3 1/2in giant Hawkfish <When all these fish grow it will be too much for your tank. You'll likely run into water quality and stress problems.> Water Conditions: Ammonia = 0 Nitrite = 0 Nitrate = 15ppm PH = 8.1 Temp = 78-81F relatively constant Problem #1 Yesterday morning on my way out to work I saw my dog whining next my aquarium. I look in the tank and my zebra moray eel is not in there. Somehow he figured out how to get out of the tank, and probably fell about four feet onto hard tile. (I have since thoroughly secured my lid) <Good, that's recommended for all moray eels and most other eel shaped fishes.> My guess is he was out of the water for at least an hour but I don't know exactly. To my surprise he was still alive all be it a bit dried up and dirty. Anyways, I grabbed him ran some fresh water from the faucet over him to remove dirt and dead skin from him. He lost a lot of skin and slime. I put him back in the tank and had to go to work. When I got home he was still alive. Actually all things considered not doing too bad. He is obviously very stressed and isn't moving around much at all, but he is able to move. Considering the skin loss he hasn't lost much color, and eyes look fine. Only the very tip of his tail is whitish probably dead skin I could easily remove but I've been trying to just leave him alone and relax. All day yesterday he was breathing very heavily. Today his breathing seems to have returned to about normal. Although he is able to move, parts of his body don't look quite right. I fear he may have some internal injuries from the fall. I'm optimistic he is going to pull through, but cant be certain. <You did everything right and also your dog seems to be educated very well, because he did not kill or carry away the eel.> Yesterday I did a 25 gallon water change so I could vacuum up any excess dead skin in tank and also I figured his recovery would be aided by as high quality of water as I could provide. <Very good.> The local fish store person advised that I put this stuff called Melafix Marine into the tank to help prevent a bacterial infection on his skin. I put the first dose in there yesterday but all the other fish seemed not to like it much. I guess my question is in your opinion do you think that I should continue with the Melafix treatment? After watching my other fish's reaction to it I'd prefer to just keep monitoring water conditions and do water changes as needed and discontinue the treatment. It says that stuff is all natural and safe to use in tank but after reading your site I'm very hesitant to add anymore of it. I would appreciate any advice you could offer on this situation. <The recovery can take several months, you'll need some patience. I would not rely on the product you are using, but rather on good water quality and, when he starts eating again (can take a while, he went through a lot of stress), a vitamin enriched, varied food.> Problem #2 For the past week or so I have been noticing that some of my fish seem to have a bit of laboured breathing. <I'm not surprised seeing your stocking list and setup.> My Hawkfish especially has been spending much of his time up near the surface and filters, also I notice the flame angel and the eels poking their heads out of the top of the water. So my concern is that my tank has poor dissolved oxygen levels. <You can bet so.> But with my eels I have to keep my tank lid tight and secure. <Right. People with morays in coral reef tanks and strong illumination often apply nets, eggcrate and meshes instead of lids.> I suspect that this may be the culprit of the poor oxygen. (Actually that may be the reason the eel escaped?) <Possible, but we'll never know for sure. Does it have enough shelter? Does the other moray or any other fish stress him out?> I really have no idea how to improve this being that I have to keep the lid closed tight. I tried putting my powerhead back in the tank to improve water flow but the currents are way to strong for my small fish. <You could get two or three smaller ones with large outlets like Koralia or Tunze NanoStream models. They'll produce a soft current, but still sufficient surface agitation.> Could you please advise me of the safest and most economical way to improve my dissolved oxygen content considering my lid issues. Is there any way to test for dissolved oxygen concentration? <Yes, dissolved oxygen can be tested (e.g. liquid test by Salifert), but usually you do not need this test. What I would do is: 1: Re-think the combination and number of fish in your tank. It should be reduced. I know this is no advice one wants to hear, but believe this will be inevitable to get a stable system in your case. 2: A skimmer will drastically increase the dissolved oxygen and also reduce the organic pollution, which additionally inhibits the uptake of oxygen into the blood of the fishes. I would modify the lid to be able to use a skimmer or install an overflow and a refugium/sump with a skimmer (see WWM re). The second possibility would be more expensive, but also more beneficial. 3. Small powerheads pointing towards the surface will increase surface agitation and consequently gaseous exchange. Small diagonally arranged holes in the back of the lid as well as opening the lid, when you are at home will help to exchange the air above the water.> Thank you again for all you help and hard work! Adam <I hope the suggestions above will help. Cheers, Marco.>

Dissolved oxygen in closed top system 7/17/08 Hello Bob and Crew, <Hello Eric, Scott V. with you.> I am going to be setting up a 125 gallon marine aquarium and was wondering how much open surface area was necessary to insure proper oxygen levels. <It can be surprisingly important.><<Mmm... unless a good deal of gaseous diffusion is occurring elsewhere... as in skimming, a sump... RMF>> I want to close the top off as much as possible to reduce evaporation. <Allowing evaporation has benefits, your tank will run cooler and some evaporation will occur with any gas exchange.> I believe having a completely sealed top would not provide enough air for surface agitation. <It won't allow gas exchange/incoming O2.> Having the top completely open obviously would. So what would the minimum surface area left exposed to the air need to be? <Quite a bit actually. Anything that limits the evaporation will also limit fresh air coming in to promote oxygenation.> I am having someone cut a glass top and wondered how much space needs to be left open. <I would personally leave at least 20% of the top open. Even with holes or thin strips open, the air flow/exchange through can be quite limited.> There won't be a skimmer to help out with aeration. <Do reconsider this, even with a low bioload a skimmer is very beneficial.> The bio-load will be kept very low. Thanks for the help. Eric <Welcome, I hope this helps, Scott V.>

Oxygen... I think, SW troubleshooting    6/27/08 Hey guys - <Hey there! Benjamin here.> For starters, you rock! We love you. <It's nice to be loved. Thanks!> I have a 110 gallon display w/ 100 #s live rock, ~1" live sand, 6x32W NO tubes, 2xpowerheads + a 20 gallon fuge w/ ~5" live sand, tons of feather Caulerpa, 65W CF + 20 gallon sump w/ EuroReef RS80 and heaters. Total flow is around 2000 gal/hr. Temp: 79, SG: 1.025, pH: 8.2, Ammonia, Trites, Trates: 0. In the display are 2 clowns, a Longnose butterfly, a powder blue tang, two skunk cleaners, two emerald crabs and a bunch of snails and hermits. Tank has been up and running for about a year. The tang is the newest addition and has only been in there for a month, but he is kicking butt and has already gone from looking like a skeleton to being nice and plump. I do a 10% water change every week. <Sounds good> All of my fish breath quickly. They always have. The butterfly probably flaps its gills twice per second. The clowns and the tang probably three times or more per second. From what I have read, this is a sign of there not being enough oxygen in the water. My problem is that my skimmer is running all the time with the air hose completely open and the overflow pipes from the display overflow box to the sump vigorously stir the surface of the water in the sump. My sump is full of bubbles. It would be hard for me to believe that I am not dissolving enough oxygen in the water. I guess my questions are: Is there any way to test the dissolved oxygen content in water? <Kits are available. Can be difficult to get a good reading, but workable> and Is rapid breathing a symptom of anything else besides low oxygen? <Can be symptomatic of nitrite poisoning> What do you suggest I do? Since I have had excellent luck with this tank so far, I really don't want to mess with anything. The fish seem to be doing great - I only notice how fast my fish are breathing when I see how slow others breathe at the fish store. One more thing, I am not sure if this is relevant, but I have always found it odd. All the fish tend to stay on one side of the tank. It is the side I feed them from as well as the side where the most amount of return water comes from the sump. It looks like the prefer to occupy about 25% of the volume of the display tank. Sometime I catch the tang and the butterfly foraging the live rock on the other side, but that's it. <Sounds like they're going where the oxygen is. For a tank of this volume the surface of the 20gal sump may not be enough aeration- bear in mind saltwater can only hold so much air, so after it reaches saturation it doesn't matter how much air is in the skimmer if it's fractionating oxygenated water. I would suggest adding a couple of medium power heads toward the surface of your aquarium, or redirecting the ones you have to increase surface agitation. A rippling surface is a surface that exchanges gasses> Thanks in advance for you help, <No problem, Al. Best of luck!> Al <Benjamin>

Re: Oxygenation - 6/28/08  7/18/08 Ben, It's been while, but I think I figured out my problem. It wasn't oxygen. It wasn't nitrite poisoning. It was Ich, possibly in combination with parasites. <Mmm...I would suspect ich as a secondary reaction to stress- possibly from poor oxygenation, nitrite, etc.> I didn't notice the symptoms until they got pretty bad and were on 3 of my 4 fish. Don't worry, it wasn't too late. I was able to net all 4 and get them into my 29 gallon QT and started treating with the recommended dosage of CopperSafe. They are all doing very well. <Glad to hear it> After only a couple days, most if not all of their symptoms have gone away. <Marine crypt. spp does have a life cycle off the fish, do read re on wetwebmedia.com> I plan on keeping them in QT on the CopperSafe for a couple more weeks, then diluting the CopperSafe via my periodic water changes for another couple weeks after that. My display is running fallow and I plan on using this time to swap out my substrate. I also picked up the 18 watt version of the TurboTwist UV sterilizer. I am running it with 100 gph of flow with hopes that this will help in the future. <Perhaps...> When I was getting the QT ready, I was worried about overloading the small hang-on canister with all 4 fish. My tang eats and poops like crazy. I decided to "sacrifice" about 10 lbs of my live rock to help out the QT as well as give my tang something to munch on. <In copper, this rock will lose its filtering properties...as will the canister. Water changes key...also, will not grow Macroalgae for the tang> My question is: Is this $80 worth of rock lost forever since it has been subject to CopperSafe treatment? <Yes...not suitable for reef use> and/or still housing Ich, etc? Could I get away with a vigorous saltwater rinse? Thanks again, Al <No problem. Benjamin>

Dissolved Oxygen and Protein Skimmers Vs Surface Agitation  6/26/08 Hello, I was hoping that you could point me in the direction of any studies regarding protein skimmers vs. surface agitation and dissolved oxygen levels. Basically which of the two is more effective. Thanks John <No time to look this up for you... Maybe some of Stephen Spotte's in-print works would reference, or off to the library: http://wetwebmedia.com/litsrchart.htm The DO is best increased at/within the skimmer though am very sure. Try it/experiment and see. Bob Fenner>

Windex?? -04/11/08 Hi there. You guys, and girls are the best info source there is period. Just a quick question. I have a 125 gallon reef ready saltwater tank. 140 # live sand, 100 # live rock. Bio rocker filter in sump, Kent Marine Nautilus Skimmer, 15 watt angstrom uv. I've had it going for almost 2 years, and I feel pretty knowledgeable in the hobby, but am constantly learning of mistakes that I have been making. My water quality is always within the parameters. Nitrate usually gets up to around 10 ppm before my monthly 15-20 % water changes, that I mix myself using store RO water from the water machine, and instant oceans reef crystals. PH is constant 8.2 in evening time, temp is steady 75, and specific gravity is around 1.023. I have a 3- 250 watt metal halide, and 4 96 watt CF lighting fixture. And glass covers on the top. My problem is that I am not able to keep more than 5 fish in the tank before they start dying off one at a time. The only fish that I've had for over a year now is a medium size Tomato Clownfish. He's superfish... But I've had 2 small blue tangs last for 3 months, than just die with no signs of Ich, Raccoon Butterfly, Naso tang, Gobies, (tank is populated with copepods), cleaner shrimp, feather dusters..... none of which seemed to have any sicknesses. Just all the sudden stopped being active and hiding, and not eating, then heavy breathing, then dead within 2 days... <Do you have any circulation in the tank? You might have low dissolved oxygen. This is just my "educated" guess, but it sounds like your fish are suffocating. Clown fish usually stay up at the top of the tank (near the surface of the water). So if oxygen (gas exchange) is the problem here, that *might* explain why the clown has survived.> I take very good care of my tank only to be frustrated by mysterious sudden deaths. My new though after doing some reading and more research is: Could I be poisoning my system by using Windex to clean the outside glass of the tank. I spray carefully on the bottom half of the tank and clean with a paper towel. I know that if it got directly into the tank that it would not be good, but then I read that even using Windex in the house could get into the system and cause trouble, and if so how do I go about ridding the system of any toxins... <I doubt it's the Windex. The toxic chemical in Windex is ammonia. I would think you could test for that.> Is that true, and even with the glass covers that I have sealing the top of my tank. <Sealed? Yikes. This might be your problem.> That's another question, every fish store that I go into they never have glass tops covering their tanks, it's always open. Does that make a difference. <Oh yes... it's important for gas exchange (so the animals don't suffocate.> I know it will cause heat to get trapped inside, but I've got that issue under control. I am running out of ideas. I know I'm not overstocking it, and I only add 1 or 2 fish at a time and monitor the parameters during that week. Please if you could help me in any way... I really love this hobby but am very frustrated at this point.. <Try taking the lids/covers off your tanks! More water circulation would also help in more ways than one. Add a good power head or two.> You guys are a great service to hobbyist all over. thank you <De nada and good luck, Sara M.>

Re: Windex?? - 4-11-08 I have 3 Hagen 802 powerheads running (right, middle, and left on top), and a Mag 7 pump for my overflow returns. I have lots of water movement on the top. But like I said, the tops have the glass covers. I was always under the impression that I would have major evaporation problems, <Yes, you will, as do all marine aquarists.> (I'm currently adding 5 gallons of RO a week) <Haha. For a tank this size, it's not unusual to lose up to 5g/day!> and bad salt creep issues on my light and tank. <There are things you can do to help prevent this. In fact, Coralife makes an anti-salt creep spray that (much to my surprise) actually seems to work (in my experience with it). It's called Salt Creep Eliminator.> Should I add a small air pump, with an air stone. <This would be a sure fire way to add to your salt creep problems without helping with gas exchange all that much.> I've never seen a saltwater tank with one. <Please consider taking the lids off your tanks. There's a good reason you never see marine tanks with them (except maybe on nano tanks). Yes, you will have a lot of evaporation. But that's just one of the things we all have to deal with.> Thanks for the ideas. Let me know if you think the tops are part of my problem, <Yes, I do... especially if they completely seal off the tops of the tanks.> and if I would have problems with my concerns. Thank you Aaron <De nada, Sara M.>

Re: Windex?? -04/11/08 I just tested my water with a red sea oxygen test kit, and came up with 7 ppm oxygen. This was from the top of the tank with the lights being on for a few hours. What is the normal oxygen level supposed to be, and does it matter if I get the water sample from the top of the tank or middle/bottom, or with the lights on or off. <5-6ppm is optimal for fish health, but these test kits don't tell you much (if anything) about your real dissolved oxygen levels. Even just the act of taking the test potentially changes the oxygen content of the sample. Yes, both depth and light would matter too.> Thank you for the help Aaron <Best, Sara M.>

Re: Windex?? -04/13/08 I retook the test with the lights being out for 12 hours and from the lower half of the tank and had the same results. Am I thinking right by thinking that with me only having one clownfish, one cleaner shrimp, and several small snails and crabs, that the O2 level is ok now but when I get 3, 4, or 5 more fishes in there that it may become a problem then since more O2 is being used by the additional fish. <Or, the additional fish are producing more CO2. Also, again, I don't think those test kits are very telling of actual O2 levels.> If that was an issue could I use my say an air pump in my sump and add more oxygen that way, along with the power heads in my tank. <::shrug:: I don't think that will help enough, but you can try it.> Also could I take off one of the three lids, or would I need to remove all three to achieve the optimal gas exchange. <Well, removing one would be better than not removing any. Or, you could take a portion off each lid.> I am just concerned with the extra evaporation, and Jumpers.... <I understand. But these are things everyone deals with. You can use eggcrate to prevent jumpers. The evaporation is harder to control. But if you have your own RO/DI unit, then you should have plenty of top off water on hand.> Thank you Aaron <De nada, Sara M.>

The Root of All Evil- Low Dissolved Oxygen 4/9/08 Guys, thanks for all of your help, my system was super saturated but I have definitely made headway. I think I finally bumped into my ultimate problem and need your guidance though, low dissolved oxygen! <A not uncommon source of trouble in captive aquatics...> Here's the setup, 900 gallon system. It consists of a display (160), a sump in the basement (150 gal), a refuge with no sand and just Chaeto (50 gal), and two 300 gal tanks. The issue is, and I never realized this when doing so but because I have a little monster (4 year old), <Ah, children... the promise of tomorrow> I removed the sump to the display a few years ago and have had weird issues since! The sump in the basement pumps directly to the display, the display has 3 400w halides, closed hood with two fans. There is 50 feet of pipe between the basement sump and the display, I believe this to be causing low oxygen in my system. Further, the sump in the basement pumps to my 300 gallon tanks through another 50-60 ft of pipe. I have big-time flow, a clean system, killer skimmer, use ozone but I am never able to get ORP above 300-325, <This... is high enough> I easily supersaturated the carbonate, a sera O2 kit is giving me a reading of 4 ppm <Low> (I don't normally buy their tests but based on all of symptoms I can believe it). System ph wont go above 8.15 (I used to drip Kalk but in an attempt to maintain 8.3 I super saturated the water). If I take a cup of system water outside and aerate it, ph rises to 8.3. <Not uncommon> Skimmers are located with the sump (if I were to draw a pic for ya the sump would be located in the center of the system, with the tanks 40-50 ft away). Finally when I take filter socks off the system, polyp extension increases big-time! <Need to clean/switch these more often... perhaps daily...> I do aerate RO and water change water. So here are my questions: I am reinstalling a sump under the display today and will be aerating it, the sump in the basement will feed the display, the display will feed the "mini" sump under the display, and a pump will return back to the display. The mini sump will also be plumbed into the return lines going back to the basement sump. I will also be doing something similar on 300 gallon tanks. Will this be enough? <Mmm, maybe...> Should I try to aerate the 50 ft drain lines themselves? <No> From reading Calfo's book, it sounds like oxygen drives ORP (obviously), ph, and buffering capability. <All so to an extent> The only other options here in my opinion would be to add smaller skimmers to each tank for maximum aeration, or to break the system into two separate systems and eliminate the 50 ft of pipe, I just had a preference one large system as it provides for greater stability (at least in theory!). Thanks for any advice, you guys kick butt! <Mmm... well... a few things to state... First, I'd definitely be "checking the checker" here... Perhaps borrowing someone, or club's, or a store's DO meter... measuring dissolved oxygen a few times during the day, night... You may be a candidate for adding more circulation (some of those spiffy in-tank pumps that mount on the side...), perhaps the adding of a large amount of fine sand in that sand-less refugium (a bunch to speculate here)... Bob Fenner>

Gas exchange... wet/dry, skimmer, tight lid, and oxygen  12/23/07 Hello and thanks for all of your great info on this site! <Hello Kevin.> I have a 55g aquarium with 50 lbs of live rock, 30 pounds of live sand, one small clownfish, and about 25 snails (Astrea, Cerith, Nassarius). I'd like to add another clownfish and some other small fish (haven't decided what yet). <Do research your selections first for compatibility with your current clown.> I have the CPR dual BakPak hang-on-back skimmer with no bio-media in it. There are two MaxiJet 1200's driving the skimmer and two additional MaxiJet 1200's for extra circulation. I used to run an EHEIM wet/dry 2229 with some of their EHEIM Substrat bio-media. The nitrate levels were around 30ppm. After reading through the FAQs on this site, I decided that the liverock should be sufficient for bio-filtration and removed the wet/dry. I'm still slightly concerned about aeration/oxygenation without the wet/dry filter. I have no airstones in the tank. I like to keep it clear of bubbles. <Yes> I think the skimmer should be more than sufficient for oxygenation, but I turn it off using a timer for about 6 hours a day since the aquarium is right next to my television and it's just way too loud. <Really? Is it suction noise? There should be a little silencer on the end of your airline, these skimmers should not be that loud.> I also think the other two MaxiJet 1200's, which are running 24/7 are probably moving the water around enough to get some oxygenation at the surface. However, I have the top of the aquarium almost completely sealed with acrylic to prevent SG changes, evaporation, fish jumping out, etc... Is the six hour daily time period with no skimming enough to significantly decrease the oxygen level in the tank? <With the top sealed up and an increasing fish load, yes.> How much of the tank lid needs to be "open" in order to allow for air exchange? Would a couple 1/8 or 1/4" holes be sufficient? <Not really, go larger, more open. > Is there some way I can use the wet/dry for the sole purpose of increasing oxygen without increasing the nitrate levels? Would running it empty do the trick or do you really need all of the surface area for promoting oxygenation? <This is a great solution for you; it will still provide gas exchange. I also recommend investigating why your skimmer is so noisy. You should not have to turn it off at all.> Thanks, and have a great holiday. Kevin <Welcome, happy holidays to you also, Scott V.>

- CO2 Injection for a Reef Tank - Good day. <Good morning.> I have been admiring your website for quite some time and I now may have a question worthy of asking you. I noticed that the area of FAQ's under dissolved oxygen  ( http://www.wetwebmedia.com/dissolvedoxygen.htm ) is empty so you may want to put this in there as it may apply. <Ok.> My question relates to adding C02 to my reef tank. <Why would you do such a thing?> If I bubble in C02 into the tank will the skimmer take it out by trying to saturate the water with another gas ( air / nitrogen and O2 )? <To a certain extent, but depending on the efficiency of the skimmer it likely won't get 100% of it.> I have a 110 gallon tall tank with an 80 gallon sump that has been divided for filtration and for macro algae growth to remove dissolved organics. I would like to inject C02 into the water to help with the macro algae growth (razor Caulerpa) I understand this will effect my PH so I would have to watch this closely. <I wouldn't recommend this. Should be sufficient CO2 from other organisms in the tank and also from the plants and corals during the dark phase. The presence of CO2 is rarely the limiting factor in algae growth but rather the other foods: phosphate, nitrogen, and potassium... [think fertilizer] which typically come from the tanks inhabitants.> I am currently looking into getting my calcium reactor going thus I may have some residual C02 in the effluent... <Usually not much... the residual amounts are typically used up very quickly by other processes, including your algae and also skimming, overflows, etc.> That may be enough to help the plants enclosed are some pics of my set-up ... I have been doing this " reef thing " for a good 10 years or so and there is still so much to learn, any comments will be appreciated. <I think the reason for slow algae growth is a lack of organics... you don't have much in your tank, and it's my guess that as a result you're not feeding much. I will reiterate, I don't think it is wise to add raw CO2 to your tank... the water will acidify and cause other problems - deplete your buffers, etc. Much better to add CO2 via a calcium reactor, where the 'reactor' will use most of the CO2. As for you the growth of your algae, I'd look to extended lighting and dissolved organics from fish/feeding to fill this gap. Give the system some time and I'm willing to guarantee that the algae will take care of itself, to the point that you'll be asking us how to get rid of it.> In the sump pic you will see a top fathom skimmer, this has recently been replaced with a modified version of the TF utilizing a air injection system before the impeller and a taller reaction tower. This modified skimmer pulls out some nice dry foam on a regular basis. The lighting on the sump is not shown either as this sump pic is an early one. I am running close to 100 watts of compact fluorescent light on the "refugium". I hope this question is worthy of your attention. Kevin <Cheers, J -- >

Dissolved Oxygen Issues?  Overheated Tank Hello crew, Ill get down to it, I know you have a ton of mail to answer. <Hello, Ryan Bowen helping today> My corals look ill. Withered and not opening. Problem is, I have never had a cleaner tank. <Clean...what a variable word!> 75 gallon with custom sump and refugium. Lighting is 2 x 175 watt MH with 2 x 48 inch actinics. Tank has been up for 7 months, and corals have been in for 3 months. 3 weeks ago, they began to look sickly. I change 5 gallons of water every Sunday and the make up water is with RO/DI. <Do you dechlorinate?> I have kept tanks for 10 years, but I have a whole new setup this time, (new house) and I have never had MH lightning before.  The tank did reach levels of 86 degrees when it got hot here, but I have managed to control it with a fan and have purchased a chiller. The temperatures here have toned down a bit and the tank has been a comfortable 76 to 79 for 2 weeks. No change in the appearance of the corals. <Well, temperature shock can easily kill the symbiotic algae living in the tissues of your corals.  A few week's recovery is on order.> The only other issue I can find is that my salinity was a bit high due to evaporation, but I have corrected that and still no change.<Salinity has a direct relationship with heat, so the heat shock is accompanied by salinity issues as well.> I have even changed the amount of time the lights were on, from 9 to 10 hours to 6 hours during this time to see if that was the issue. <Leave it alone, your corals will respond better to predictable lighting times.> I also changed the 900 gallon per hour power heads in the tank to Visi jets 900's. much lower flow. My green star polyps and blue mushrooms look great, and all fish and shrimp look fine in the tank. Fish consist of a yellow tang, 1 Perc, and a couple of green Chromis. (didn't want to have a stocking issue). What am I missing? <Skimmer?  Calcium and alkalinity?  Dissolved oxygen levels too low?  What's your pH?  I need more to work with, sorry> I would appreciate some advice, I can't seem to locate anything else that I should be checking. I even broke down and re-read Sprung's bible to see if I could glean anything that I could have overlooked. <I'd test dissolved oxygen, it sounds like you're overheating because the surface of the water isn't turning over fast enough, keeping oxygen high and heat low.  Read, test, re-write me! :http://www.wetwebmedia.com/dissolvedoxygen.htm> Let me know if you can. Quinn.

- Adding Pure Oxygen - Hello again there fellers, all of your help has been truly welcome.  I have a question concerning the addition of oxygen to my tank by way of bubble counter into my skimmer to combat the CO2 build up that has been accumulating in my house since it is cold out and I have to keep my house closed.  My pH drops when I have my house closed because of the build up of CO2 and have tested for this specifically in the past.  Don't have the issue in the summer because my windows are usually open a lot.  Would it be unwise to add oxygen to my tank via a bubble counter hooked up to my skimmer for the added oxygen? <Hmm... I'd say adding pure oxygen could cause some problems - oxygen toxicity being my primary concern but also excess oxygen outside of the system. Chances are pretty good that any oxygen you add will bubble to the top of the tank without reacting with anything and instead going into the atmosphere. You're better off just using a bubble wand and an air pump and relying on regular air. The bubble action should help drive off some of the excess CO2. You might also want to develop an algae-based refugium under 24 hour lighting where you would have willing consumers of CO2.> Maybe one bubble per 5 or 10 seconds or more or less?  What would be the negatives if any? <Increased ability to combust and/or oxidize items in your home. But more so, that while good-intentioned, this will not produce the affect you desire.> Would this not increase the oxygen and counter the CO2 build up? <Sounds good in some ways, but the air we breathe is not pure oxygen - it's about 21% oxygen. Adding pure O2 is asking for trouble. Likewise, O2 is chemically very stable, so it's not very likely that it would react with anything in the tank, meaning you would still have roughly the same amount of CO2 in your system.> I have access to an Oxygen tank and would need to buy a solenoid and bubble counter.  I have quite enough water flow in my tank and am using a Euro Reef CS6-1.  It's a 180 gallon.  It pulls out massive amounts of gunk and have to clean it at least 1-2 times per week.  I have a lot of SPS along with a few LPS and softies.  Yes, I agree big load but am concerned with keeping the pH up.  I add Kalk daily at night which boosts the pH up from 8.06 to 8.3 at the most.  Also have a calcium reactor that does quite well at keeping the calcium and alk in tune.  Any thoughts on the cautious addition of oxygen? <You got 'em.> Thanks again, Jeff <Cheers, J -- >

-O2 addition to combat CO2 buildup- Hello, I have been e-mailing the below question to you for the past 3-4 days with no reply from you fine folks.  I searched your web site but didn't see the answer to the question I sent.  Please try to respond sometime soon. <I apologize for the delay, but unfortunately we don't have unlimited time and must answer emergency type questions first.> You are probably swamped with questions and haven't had a chance yet to get to it.  Thanks again, Jeff Hello again there fellers,<Yo! Kevin here> all of your help has been truly welcome.  I have a question concerning the addition of oxygen to my 180 gallon tank by way of bubble counter into my skimmer to combat the CO2 build up that has been accumulating in my house since it is cold out and I have to keep my house closed.  My pH drops when I have my house closed because of the build up of CO2 and have tested for this specifically in the past.  Don't have the issue in the summer because my windows are usually open a lot.  Would it be unwise to add oxygen to my tank via a bubble counter hooked up to my skimmer for the added oxygen? <Unless you have horrible gas exchange, there should be no need for oxygen additions. It is important to note up front that the concentration of O2 in the water does not effect the CO2 levels.> Maybe one bubble per 5 or 10 seconds or more or less?  What would be the negatives if any? <I cant see any, besides it being a fire hazard.> Would this not increase the oxygen and counter the CO2 build up? <Nope> I have access to an Oxygen tank and would need to buy a solenoid and bubble counter.  I have quite enough water flow in my tank and am using a Euro Reef CS6-1. I had a CPR SR9 but was not too impressed with the amount of dissolved organics that it was pulling out.  Bought the Euro Reef for an incredible discount from a friend who bought it brand new but never used it. <Sweet!> It pulls out massive amounts of gunk and I have to clean it at least 1-2 times per week.  I have a lot of SPS along with a few LPS and softies.  Yes, I agree, big load but am concerned with keeping the pH up.  I add Kalk daily at night which boosts the pH up from 8.06 to 8.3 at the most.  Also I have a calcium reactor that does quite well at keeping the calcium and alk in tune.  Any thoughts on the cautious addition of oxygen? <How about either installing a second chamber on your calcium reactor to hopefully absorb any excess co2 or somehow connecting the drip line from your reactor to the mixing portion of your skimmer (AquaC does this on it's larger EV models) to blow off excess co2.> Also, do you recommend the use of Red Sea salt?  I can get a 200 gallon bucket on sale for $31.99 which is cheaper than the same 200 gallon bucket of Instant Ocean that I always use.  Not sure if I should take the risk or just stick with what's been working for me for the past few years. <Well, if it ain't broke, don't fix it I suppose. I'm not a big fan of red sea salt, but have since forgotten why (haha, I know, I know!). Sorry, it's late! -Kevin> Thanks again, Jeff

Oxygen Saturation Question - Emergency Plans >Hi Crew: >>Hi Gregory.  Marina today. >Really quick question for you...not sure about the answer though.  All the power problems and storms on the East Coast recently have made me think of emergency planning.  (Just because I'm paranoid does not mean that there is not an international conspiracy to kill my fish!!)  Do you know (or can you point me to a book/article discussing) the approximate time that it would take a given amount of fish to lower the oxygen saturation in a tank to fatal levels?  I know this is impossibly complicated but I'm just looking for some sort of ballpark range (hours/days??).  If it helps to be specific, I have a 110g with three 4/5-inch tangs, two 4-inch butterflies and a Centropyge angel.  I assume that they could last quite a while in this tank, but I may be wrong. >>Indeed, just saw a query from someone who lost his fish by the end of the day (8-12 hours, if I recollect correctly) due to pump failure.  Different catastrophe, same result.  Good idea to plan. >I read through the fax about oxygen, but didn't find anything discussing this sort of timeframe.  As always, thanks for your time and experience.  BTW, I'm really enjoying the little messages about NMA V2.  Must be alternately exciting and wearying to be working on such a project.  Take care, Gregory Fickling   >>Absolutely, I'm hoping my contributions to the previous tome were well received and might be taken advantage of again.  ;)  I suggest you go to a bait shop and buy several battery operated air pumps.  These tend to be both cheaper and more powerful than those you might find at your LFS.  Unless, of course, you can afford to and have a place for a generator.  Marina

Science Project Help Dear Crew: My daughter is doing a science project attempting to prove that a plant adds oxygen to its environment using gold fish and their environments. My husband wrote to you when we began this requesting information on testing the O2 levels in the water.  We were unable to find the test kit you recommended and none of our pet stores could order it. <Try the etailers... listed on our links pages on WetWebMedia.com> Is there another way to tell through the behavior of the fish?  Is it possible there is a good website out there regarding goldfish behavior in relation to the oxygen level in their bowls? <Would have to search... the same as you or your daughter> This thing is due Tuesday and we are about to pull our hair out.  Everything we have found has been on pond gold fish or behavior when chemicals were used in the fishes environment. We have tested nitrites, ammonia and ph levels daily for this experiment.  Is there some way to prove a correlation between our results for those levels and the amount of O2 in the bowls? <If you can rule out other factors... Bob Fenner> Thank you for your help. Cheryl Conrad

- Oxygen Testing - Crew, <Good morning, JasonC here...> My 3rd grade daughter is performing a science project involving oxygen replenishment in fish tanks. She has set up 3 2.5 gallon bowls with goldfish. One is fed from a whisper pump, one has an Amazon Sword plant, and the third has no outside oxygen source. My question is where to direct her to find testing procedures to validate her research. She is from a gifted cluster class and has a very good grip on science. Can you recommend an avenue to explore please. <Sure... there are test kits for dissolved oxygen available, although they may not be in stock in your local fish store, they can be ordered there or online. The Salifert kit will probably be the most economic.> Thank you for your consideration. Steve Conrad (Science assistant dad) <Cheers, J -- >

- Dissolved Oxygen Problems? - I need some major assistance on getting more dissolved oxygen in to my reef. <Oh?> I have had problems with fish lately.  They showed signs of oxygen depletion before dying suddenly. <Could be signs of something else...> There are droves of xenia, sps, clams, lps, and polyps that are doing great and multiplying. <So... they need oxygen too...> I suspected oxygen issues so got a Salifert O2 test and it read at 5 and needs to be 9 or higher. <That might be more an issue of waiting another minute to do the test - natural sea water is about seven PPM... so you're not really that far off.> Let me tell a little about the system.  It is a 75 gallon Berlin.  The is 90 lbs of premium liverock, 2 175 watt halides, 2 100 VHO actinic, an ETSS 600 skimmer, with 2 GenX pumps.  The tank circulates around a 1500 gallons an hour and 500-600 through the skimmer. <Yeah... with a skimmer, it's REALLY hard to have problems with dissolved oxygen.> The skimmer has been tweaked and runs great.  There is a powerhead on the left side of the tank pushing against the return.  There are 2 returns and they are near the surface.  The surface of the water has major agitation.  There is a 36 watt UV in the sump (sump has liverock only) (Could the UV be breaking down the O2?) <Not a possibility.> There are many types of macro-algaes growing in the tank. (Co2 build up at night?) <I really doubt it - it would be hard to get into that much trouble, but this you can test by cutting back some of the algae.>   I need major help.  Ideas of equipment and such.  I thought the big skimmer would do fine.  I have tested the O2 many times during the day and it remains the same.  There is a lot of coral and two fish, but not too much.  I cut back the xenia and Sargassum majorly.   I had Chevron, Asfur, Sunburst, and pygmy fireball, but they all died in 4 days when I added the last two. <Did you quarantine the fish before you added them? Could be you introduced some Amyloodinium...> Then after a long wait I added 3 yellow tangs and the same happened. <All at once? My friend, I think your problem are more in your methods for introducing livestock than with dissolved oxygen.> The water is crystal clear and all chemistry is in line.    I also have a 1/4 hp chiller that sticks the tank at 76 degrees. Please shed any light you can on the situation; my hobby of 20 years is becoming a nightmare quickly as my fellow hobbyist friends give me major grief. <Look deeper... the answer is there somewhere, but I still think that dissolved oxygen is a bit of a red herring.> Thanks for all your advice on the web, Lee Larson <Cheers, J -- > Re: Reference to dissolve O2 Hi Bob I did not spell check my E-mail before I sent it.  In the message )2 is supposed to be O2 (oxygen).  Sorry I got trigger happy. Thanks, Lee Larson <No worries. Cheers, J -- >

- Testing for Oxygen - Hello again crew <And hello to you.> I have yet another question about my tank. How can you measure the oxygen in your tank, is there a special tool like the hydrometer or something or can you just tell by all the bubbles floating around in the water? <There are test kits for this, although they are rarely seen - they can be ordered.> Thanks again. <Cheers, J -- >

Dissolved Oxygen/ GBD >Gentlemen, >>And ladies, thank you.  ;) >>O.K., I've read every post about gas bubble disease and dissolved oxygen yet I still need help :) >>As I understand it, it's not necessarily dissolved O2, but any supersaturation of dissolved gases (say, 110%-140%) held within the water.  That is to say, when you see actual bubble formation, the gas is coming out of solution into the water column, and not into the fish. >Now, a certain amount of dissolved oxygen is good but too much could lead to gas bubble disease right? >>Technically, correct.  Remember, this is not peculiar to dissolved O2. >I have a Mag 7 as my return pump from my sump to the main, and it was spitting out a lot of tiny bubbles into my tank. After further reading, I realized that too many tiny bubbles was bad, so I sealed the leak that was causing it (check valve). Now I still have a small amount of tiny bubbles from the return line but there is no air leak to be found. Is this small amount acceptable? >>That can best be answered by your fish.  If you're really worried about it, then breaking the water flow up (any type of "waterfall" effect, for instance) should cause all supersaturated gases to come *out* of solution.  So, you could, for instance, have the return line set just at the water's surface, but angled up so as to force a bit of a waterfall (but without causing splashing, which leads to salt creep). >I read that sometimes air can be introduces into a pumps impeller housing which would be dangerous. I did let my Mag 7 run "semi-dry" for about 1/2 a second when I was first trying to get the plumbing right. Could this be the cause? >>No, some sort of cavitation (as seen with boat propellers) would be more likely.  Once you've got any air pockets worked out initially, you should be golden. >I've also noticed that my Magnum HOT filter spews out a bunch of air bubbles in short intervals once in a while. Is this something I should be concerned with? >>My guess would be cavitation, again.  As I mentioned earlier, if you are getting actual bubble formation it means that whatever gases that are being held in solution are coming *out* of solution.  Again, if you're concerned about it, find a way to diffuse the water flow and break up its contact area (=surface area) interface with the air. >How mush dissolved oxygen is ok/ needed? >>Aaahh.. now we're getting back into that chemistry my son has been throwing at me!  I really wouldn't worry about the situation unless you're seeing fish demonstrating symptoms of Gas Bubble Disease.  Do a Google search (I've also just learned of http://www.googlism.com --haven't used it yet, but what the hay) and you'll get *many* hits.  Here's a really useful one I just found--> http://www.reefs.org/library/article/cripes_kowalski_phipps.html >Much thanks, Greg >>Quite welcome, Marina.

Re: Dissolved Oxygen Good Afternoon. <J.T.>     I have had a problem (since I started my aquarium in August of this year) getting an acceptable level of dissolved oxygen. It has typically been in the 4 mg/L range. All other parameters are perfect. I run my tank at 77 degrees F. and at a specific gravity of 1.024. We left the tank unattended this past holiday weekend (Thanksgiving). Since it was an extended week-end combined with the  fact that I have removed the lid from the tank, have a tank turnover of approx. 25 times per hour and I have arranged my pump returns to achieve turbidity at the surface, I experienced a high degree of evaporation. With the lowered water level, one of my pump returns was causing so much turbulence at the surface as to almost splash water out of the tank. I figured that this would have helped to raise the dissolved oxygen level. I checked my parameters and all is well (s.g. was in-between 1.024 & 1.025 due to the evaporation) but dissolved oxygen was only at 5 mg/L.       I know one of my problems is due to my tank design. I have a 45 gallon tall (12"D x 36"L x 24"T) which only gives me 2 square feet of surface area. I have been assured that my skimmer is properly sized (a CPR Bak-Pak 2R). After extensive reading at the Wet Web Media site, among others, I have to assume that my skimmer isn't working properly. I am only getting approx. 2-4 ounces per day our of my skimmer trap. <This may be... all there is> The water is a green/dark green in color with the "foul" odor everyone speaks of. Everything I read makes me believe the skimmate should be a coffee color and I should be producing more. <You might be able to adjust the amount, fineness of the bubbles... raise the contact water level... in an effort to collect more, different make-up skimmate> As a matter of fact, when I returned home from the long week-end (4 days) I only had approximately 4-6 ounces in the collection cup. I have adjusted the cup up and down attempting to get a better skim and am what I feel is the best point. I have the venturi air valve (attached to the Rio 600 power head) wide open to produce the highest amount of bubbles. I've actually removed the plastic valve screw allowing the venturi to run wide open.     My bio load is fairly light. I have a medium Yellow Tang, small Flame Angel, medium squamosa clam, medium frogspawn, medium leather umbrella coral, small xenia (pom pom) and the clean-up critters (scarlet reef hermits, Cerith snails, Mithrax crab, cleaner shrimp, banded leg crabs, queen conch, abalone, serpent star, brittle star & Margarite snails) Any other suggestions how I might be able to get my oxygen level up? <It might actually be nearer to saturation (about 7 ppm) with the difference lying in the test device... But, perhaps adding a mechanical aerator near the bottom (an airstone) at one end of the system, will help to turnover your water more completely, rendering more of the unsaturated water at the air-water interface. Bob Fenner> Thanks for all of the help.  J.T. Craddock

Re: pH alk? Anthony, you are the man.  <immodest or not...its sure nice to hear it :) Thank you my friend> check this out. My pH was 7.93 when I put my probe in my tank. I then opened a window and within 2 hours the pH was 8.16.  <yep...amazing isn't it. An interesting dynamic of modern housing (and better insulation) on aquaria> the lights had been on for 4 hours, so I wasn't sure it was the normal pH increase. the lights are scheduled to be on for another 8 hours which would mean the pH should keep going up if it was a normal daily fluctuation. to make sure your theory was right, I closed the window and watched the pH drop .06 within an hour. Pretty weird, huh? <amazing...yes. And it dropped at a time when it should have been going up confirming our suspicion> my apt is 950 sq ft. and air tight. now I'm gonna do a big water change and try to figure out how to crack a window and not go broke running a/c full bore. thanks again, Neil <best regards, Anthony Calfo>

The Conscientious Marine Aquarist (trigger feeding, high DO) I love the book and am learning tons, Thanks. A couple of questions. 1. I have a 48 gal. tank w/ one damsel, four clowns and a Niger Trigger (much larger than the clowns and damsel but all living peacefully together) and I feel the trigger wasn't getting proper nutrition from basic flake and frozen Emerald Entree so I bought regular store bought shrimp - is this ok to feed the trigger? <Yes> 2. Is there a possibility for too much oxygen in the tank? <In some unusual circumstances, yes.> Thanks, Jake-Dallas <You are welcome. -Steven Pro>

Dissolved Oxygen Working on raising my dissolved oxygen in my 30 gallon q-tank. Anyhow, it has a MJ1200 powerhead, a AquaClear Power filter, and a remora pro (Mag 3) skimmer on it. I just put a moray in there for quarantine for three weeks, but it looks like its gulping for air a bit. It's a slow gulp, so not like its gasping. Did a dissolved oxygen check and it shows about 4ppm, so I wanted to raise it.  <yes... rather low indeed. Nice to be 6ppm or higher> Anyhow, I don't use the MJ1200 aeration tubes (usually the skimmer on my larger tanks handles the oxygen for the tank). Anyhow, do the aeration on powerheads (bubbles) actually help dissolved oxygen, or it just bubbles and its marginal improvement ?  <yes. helpful> Wouldn't that cause the tiny bubbles that bad for fish ?  <unlikely to become supersaturated> Whets the best way to increase the oxygen in the water for inhabitants ? <ozone on a QT tank is ideal with a controller. O2, RedOx increase, disease control, water clarity, etc> Thanks Ed <always welcome, Anthony>
Re: Dissolved Oxygen Anthony, follow up on this. Before I receive the ozonizer, what would be the best way to raise DO from 5ppm ?  <water circulation that brings water from bottom of tank to the top> I have a small power filter in there (tiny Duetto) which acts like a PH at 100gph.  <rather weak water flow> It has an air adjustment as well. When you turn the air knob, it outputs fine bubbles, at wide open, its almost frothy. Also a MaxiJet 1200, with airline hose. That obviously outputs larger bubbles. I have the Duetto pumping water above the water line (more surface agitation), and the 1200 just underneath the waterline with air bubbles. <bubbles are not as effective at oxygenation as a fast turnover of tank water from circulation (top to bottom)> So, are smaller bubbles better (frothy) from the Duetto better, or larger bubbles from the MaxiJet better ?  <neither...above> Or should I just keep the Duetto return above the water, but not frothy. I have tiny bubbles everywhere in my tank right now trying to increase the DO, as you indicated that it won't be supersaturated. Makes for a bit cloudy tank though :-). <bubbles are also quite irritating to some fish and coral... just improve or redirect water circulation in tank... bubbles if the fish don't seem to mind them> Thanks, and have a good weekend. Ed <thanks kindly, Anthony>

Become a Sponsor Features:
Daily FAQs FW Daily FAQs SW Pix of the Day FW Pix of the Day New On WWM
Helpful Links Hobbyist Forum Calendars Admin Index Cover Images
Featured Sponsors: