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FAQs on Marine pH, Alkalinity, Science

Related Articles: pH, Alkalinity, Marine Alkalinity, Synthetic or Natural Seawater, Water Changes/Changing, Understanding Calcium & Alkalinity, The Use of Kalkwasser by Russell Schultz,

Related FAQs: Marine pH, Alkalinity 1, Marine pH, Alkalinity 2, Marine pH, Alkalinity 3Marine pH/Alkalinity 4, Marine pH 5, Marine pH 6, Marine pH 7, Marine pH 8, & FAQs on pH: Importance, pH Measure/Test Gear, pH Controllers & pH Buffers/Buffering, pH Anomalies (Troubleshooting/Fixing), & pH Products by Name, Manufacturer, & Marine Supplements 2

pH, alkalinity/acidity AND biomineral content (Calcium, Magnesium et al. combinations) are all dynamically interactive... As are dissolved gas (O2, CO2) effects. More/less of one affects the others...

Several Issues... Refugium effects on water chem., damsel aggr.    11/30/07 Hi Folks, <Hello> Once again I need to solicit your help. I fear it's becoming a habit :-). I installed a hang-on refugium about 3 weeks ago. These are some of the changes that have occurred: 0 nitrates & 0 phosphates YIPPIE!!! Now for the bad news... my dKH has plummeted to around 6.7 (an all time low tis usually around 8 dKH), calcium dropped to 300 ppm (it's usually around 340 ppm), my coralline algae is dying, and I have a major green hair algae bloom. Do you think the negative changes are related to the new refugium (which houses Chaeto & Caulerpa and a few mini brittle stars)? <Mmm, there is a very real possibility that the algae there are indeed malaffecting the water quality values listed, and mal-affecting the coralline, yes...> In addition I began adding parts A&B on Monday. Since then my dKH has risen to 7.9. However, my calcium is still hovering around 300 ppm. <Need to increase this component, source> BTW my PH is 8.31 (pre A&B my PH was 8.22. Any ideas on what I can do to resolve my numerous problems? Tank config: 90 gal reef, 20 gal sump, skimmer, live rock, live sand, soft corals, inverts, 8 fish, 2 BTA (and a partridge in a pear tree). Params: 0 nitrates, 0 nitrites, 0 ammonia, 0 phosphates, ph 8.31, dKH 7.9, calcium 300, salinity 1.022. <This last is low... I would increase the spg to near seawater strength. And read here: http://wetwebmedia.com/marine/maintenance/index.htm scroll down to the trays on alkalinity, calcium... read the SubFAQs files on Troubleshooting> Second unrelated problem. I have a Blue Damsel (I now know, not a smart move) who is harassing my Royal Gramma I believe to death. The Gramma was living in one of my rocks, until a couple of days ago when my Brittle Star decided to take up residence in said rock. Now the Gramma is out in the open and being completely terrorized. He looks pretty battered. Do you think it would be ok to move the Gramma to my 5 gal hang-on refugium? <Yes... that or the damsel... Who should be removed anyway. Bob Fenner> Thanks, Jacque

Re: Several Issues... Refugium effects on water chem., damsel aggr.. NealeM, pls    11/30/07 Hi Bob, <Jacqueline> Thanks for the quick response. I have read many sources in WetWebMedia regarding alkalinity, calcium, & PH. Most appear to be over my head. <Rats! I recognize that "pride comes before the fall" (with not much space between), but I do pride myself on being able to explain even arcane subjects (which our hobbies have aplenty) to folks...> Is there any info available for those folks who need it explained on a different level? <A different level? I don't even sense what I might do here... Am going to ask Neale Monks here... who is very sharp, much younger, and has a different "experience set" than I, to give this a go...> Also, should I remove the Chaeto & Caulerpa from my refugium? <No, I would not... Unless there's a "whole bunch" of it... in which case I'd thin it out... otherwise, perhaps cutting back the light intensity, duration daily will avail you... I WOULD purposely increase the alkalinity AND biomineral content of your water... via a/the two-part system or other means you have at hand and feel comfortable with... Slowly... by increasing doses a bit daily...> Will that cure my green hair algae bloom and coralline die off? <These successive approximations should do so over time, yes> Or is there another way to fend off the dreaded green hair algae. I currently perform 30 gal water changes every other week. Can you offer any recommendations where to purchase a better quality of macro algae? <Mmm, w/o getting too involved here, and not knowing the type/species/cultivar of Caulerpa... I'd replace it with either nothing, or with a species of Gracilaria (Ogo)> You mentioned I should increase part A&B to help increase my calcium level. I'm somewhat concerned that increasing the dosage will significantly elevate my PH which is currently 8.32. <Actually... the commercial products I'm familiar with won't do this... they are comprised of buffers that "hold" the pH no higher> Would you recommend just increasing the part B dosage? <Yes... worth trying. Again, just an increment more per day...> Thanks, Jackie <You are on the cusp/border of great understanding, self-realization here Jackie... I am very pleased to live vicariously through you. BobF>

Re: Several Issues... Refugium effects on water chem., damsel aggr.. NealeM, pls  11/30/07 Thanks for the quick response. I have read many sources in WetWebMedia regarding alkalinity, calcium, & PH. Most appear to be over my head. <Rats! I recognize that "pride comes before the fall" (with not much space between), but I do pride myself on being able to explain even arcane subjects (which our hobbies have aplenty) to folks...> Is there any info available for those folks who need it explained on a different level? <A different level? I don't even sense what I might do here... Am going to ask Neale Monks here... who is very sharp, much younger, and has a different "experience set" than I, to give this a go...> <<Hello Jacqueline, Bob. I have to be careful here as I'm not completely up to speed on marine aquarium water chemistry. But at a first pass, I think Jacqueline might find my intro to freshwater water chemistry -- http://www.wetwebmedia.com/FWSubWebIndex/fwh2oquality.htm -- a worthwhile read. Very broadly, alkalinity is the ability of water to neutralise acids. Since all aquaria have a natural tendency to become acidic over time, alkalinity is important. Alkalinity is chiefly provided for by calcium carbonate and bicarbonate salts (the ones measured using your carbonate hardness test kit, typically in degrees KH). This is different to general hardness, which is a measurement of other dissolved minerals of less significance in terms of acid neutralisation. As carbonate hardness goes up (for example by adding calcareous material to the aquarium and/or filter) then the alkalinity will go up as well (meaning acidification will slow down) and the pH will consequently remain stably in the basic range of the scale (typically around pH 8.2 or so in marine tanks). Most confusion between pH, alkalinity, carbonate hardness, and general hardness come about because people don't fully appreciate that they are all measurements of different things. Once you understand that, you can then see how they are connected to each other, and then more clearly see how altering one aspect affects the others. E.g., tanks with low alkalinity have an unstable pH but this can be remedied by raising the carbonate hardness. Does this help? Neale>> <Ah, excellent. RMF>

Reef Lighting... effect on pH, and in defense of Cerianthus mixing   9/20/07 I wanted to know what effects you may have experienced with PH while changing the color temperature of your metal halide bulbs? <Generally boosts pH a bit... a tenth of a point of two... for a short while> I have a 75 gallon tank, 100 lbs of sand, 100 lbs of live rock, ph 8.3, and 0 ppm on ammonia/nitrites/nitrates/phosphates. I dose with Lime water about 2-3 times a week. I use 2X 10,000K Current USA metal halide bulbs. Everything is fine while using these bulbs. When I try to change to 14,000K Phoenix bulbs, my PH drops to the 7.9 - 8.0 range. <Mmm, whatever the photosynthetic component of your systems' biota is, it doesn't like the change evidently> I have to constantly (almost daily) use limewater and Seachem reef buffer to maintain 8.3. When I change back to the 10,000k's, my PH is back to normal. I have corals of all types in my tank and you might say that the tank is medium to heavily stocked. Is the color temperature THAT important to photosynthesis and using 14,000k's means that I have an excess of CO2 because is the lower PUR of the bulbs? <Could be, yes> Also, I think that tube anemones (Cerianthus) get a bum rap from you guys. I have had 2 for over two years now and they have never exhibited the traits that you mention in your articles. I believe the dangers are blown out of proportion: <Thank you for your input here... My experience has been different> "Re: Many Questions! Tube or other Anemone ID, Missing fishes/Mithraculus 5/25/07 The anemones are Cerianthus. They are placed away from any other life, <Doesn't actually matter how far...>" and "I did read further and need you to clarify. These Cerianthus can release stinging cells into the water at anytime and therefore create death to other living organisms. <Yes> They potentially can kill off my tank without ever touching anything? <Yes> " I have never seen them release nematocysts, causing the death, destruction, and mayhem that they purported to cause. They have never eaten a fish, corals don't mysteriously get stung or stressed, and they have never killed a tank mate (coral or fish). I have seen my purple tang with light marks (where she got stung) on her, but they clear up within a day and she has since learned to stay away. I feed them twice a week and they are as happy as can be. The only problem I have ever encountered is when I first purchased the tube anemone, the sand was not deep enough and it decided to go for a swim around the aquarium. It stung a green hairy mushroom pretty bad, but it recovered and it has multiplied many times since. The tube anemones are now in a 4 inch sand bed and they don't leave their tubes. I know that others feel the same way: http://www.advancedaquarist.com/issues/june2004/invert.htm Thanks.

pH Woes 3/20/04 Hello Adam or similar: <Hi Shannon.  Similar is out for the weekend, so Adam here<g>.> Per the long thread below, the results of the outdoors aerated pH test were very surprising. Before, in the tank, my meter registered about 8.05-8.14, from AM to PM, of course. Taking a glass of water outside and aerating it for about an hour, my meter said 8.53! <Wow!  Convincing evidence that you have CO2 accumulation.> Also, measuring a glass of tank water after TMC's Bio-Calcium was added showed the pH drop to 6.9 or so. This would make sense since it is essentially liberating CO2, which is acidic ... but I assume that if tank water was properly alkaline and the Bio-Calcium added at the recommended level, then the overall tank pH should stabilize back to where it was, given the buffering capacity of the water? <Hmmm.... Tricky to explain, but here it goes...  Your explanation is correct.  Adding bicarbonate raises alkalinity, but also initially lowers pH because of the CO2 that is liberated.  The pH will rise back to normal as CO2 dissipates to the atmosphere, not because of the pre-existing alkalinity.  Without getting into the complex chemistry...  CO2 rising and falling affects pH, but does NOT affect alkalinity.> One final note - my tap water is 8.3 straight from the faucet, and relatively hard to begin with ... perhaps this has something to do with my issues?  Thanks once more, SLC <If you are using your naturally hard tap water without RO and or DI filtration, there is no doubt that it will contribute to calcium and alkalinity.  In fact, many folks using hard tap water don't add any other calcium or alkalinity supplements.  Best Regards.  Adam>

Top Off Question (5/2/2004) There is a ton of information about buffering top-off on your site, but not specifically what I am looking for.  I just got a RO/DI today, and am trying to figure out the best way to buffer my top-off water.  I use B-ionic, and thought about just using the alkalinity half to buffer (I seem to always have more of the alk part anyways).  Is this a good idea? <Seeing how theoretically the end product of an RO\DI unit should be just pure water, at a pH of 7.0, with no buffer capacity to speak of, the alkalinity buffer is a necessary additive.  However, you will probably also want to add a pH buffer to bring up the pH of the water.  You shouldn't need to add the calcium half if your tank doesn't require the extra calcium, as long as you follow the dosing instructions for the alkalinity half of the B-Ionic>  Should I buy some of that Kent Osmo-prep stuff? <I have had no personal experience with this product, but Kent marine usually makes good quality additives.  However, your current B-Ionic should work fine>  Do I just want to put a little in to get the pH moving in the right direction, or should the top-off water have the same alkalinity as the tank water? <It should preferably have a slightly higher alkalinity, and should most definitely have the same pH.  However, adding an alkalinity supplement will not directly affect your pH; unless it has other buffers as well> If I use b-ionic to buffer alkalinity for my top-off should I add less to my tank on a daily basis? <This totally depends on your system's total alkalinity.  Purchase an alkalinity test kit and monitor results to determine the correct amount of additive needed>  I could just add all my alkalinity solution for the week to my auto-top off container (a powerhead on a float switch in a 4 gal Rubbermaid container). <Once again, be sure to measure your alkalinity and dose accordingly>  I have a 55 gallon and use tropic Marin salt which I believe will mix up fine for water changes without buffering the water first.   Thanks, <No problem> -Ken <M. Maddox>

Alkalinity I have had a 75 reef tank for 9 months. My corals have done ok. I add Kent liquid calcium daily. I recently heard from someone that adding calcium lowers Carbonate Harness/Alkalinity. What is Alkalinity.  Should I start testing it. >> IMO, yes, all reef keepers attempting to house/grow biomineralizing life forms (e.g. hermatypic corals, photosynthetic gorgonians...) should measure Alkalinity... variously defined as Carbonate hardness or Acid binding capacity... and measure most frequently as dKH (often KH in the west) or milli-moles per liter...milliequivalents per liter or mg/l of CaCO3... these are all ways of looking at the same phenomena... a concentration or capacity to resist downward movement in pH if you will.... and supply needed carbonate for metabolism... And, it's not so much that adding "calcium" by itself that lowers carbonate/alkalinity, but the format in which it is added... Most notoriously the addition of Kalkwasser, Calcium hydroxide in a carbon dioxide (high pH) deficient system... will likely precipitate out the carbonate as CaCO3... The desired reaction of adding Kalk: Ca(OH)2 + 2CO2 <> Ca(HCO3)2, Calcium hydroxide plus carbon dioxide becomes/unbecomes Calcium bicarbonate... using carbon dioxide in the forward rxn, and elevating pH consequently... but at higher (normal pHs for many marine systems... especially ones w/o CO2 infusion... you'll start to see why I'm such a HUGE fan of calcium reactors employing carbon dioxide infusion:) CA(OH)2 + CO2 <> CaCO3 + H2O, the Kalk and Carbon dioxide in the water (from whatever source... becomes/unbecomes calcium carbonate (precipitate) and water... What often becomes of folks fallaciously pouring in supplements that are mutually incompatible... Bob "who wishes we all had a grasp of simple chemistry, or that he had the big bongo bucks from mis-used supplements" Fenner And who realizes that all this may "seem Greek", and apologizes for any added confusion, but could/would not answer this query in any other way

Alkalinity Bob: I have another question, this one re alkalinity. I have a strange problem which I only recently noticed when I decided to check my pH and alkalinity.  My pH is quite high, although stable, at 8.6. But my alkalinity is quite low, at 1.1-1.7 ppm according to my test kit. I checked various books, but there's no discussion of high pH and low alkalinity. My pet dealer is also stumped. What would you advise? Is this harmful to my tank inhabitants? The only change I've noticed is that my leathers have been closed more  frequently.  Thanks for your help -- Matthew  >> Hmm, let me guess... you use Kalkwasser (calcium hydroxide) solution regularly...? You're experiencing the all-too-common experience of inadequate carbon dioxide, too much Ca(OH)2 being added too much too soon... exhausting available carbonate, (if there were any) carbonates.... raising pH in the process...  There are two other (much less common) scenarios that produce the same relationships between pH, alk., and calcium concentrations... but I'll stick with this guess. And yes, this is an unhealthy set of conditions... You DO want something resembling natural sea water (NSW)... a pH of 8.2 or thereabouts, calcium of about 400 ppm (plus, minus 50 ppm or so) and alkalinity in the 4,5...8 milliequivalents per liter... All best achieved by calcium reactors... can be achieved through dual type additives... only very rarely with Kalk.... Bob Fenner, who would/does advise a thorough investigation into alkaline earth/biomineral phenomena and their relationship with alkalinity... and an established program of using additives or skipping ahead a few years to where most everyone is using calcium reactors.

Re: Alkalinity Bob; you're absolutely correct that I overdosed Kalk solution. I will look into the calcium reactors you recommend. Meanwhile should I do a big water change?  >> Ah, amazing, eh? Yes to the big water change...  Bob "Sherlock" Fenner

I have a 125gal reef tank that always seams to be a bit short on alkalinity.. what's the best way to raise it with supplements? >> >> Hmm, this is a deceptively difficult question... Let's see... it really depends on how you're raising your biomineral content and pH... and the use of other materials in your system...  A most-likely scenario: If you're using Kalkwasser... dripping it in slowly, at night... and not depleting (therefore) the carbon dioxide in your system... You can easily boost alkalinity by the simple addition of baking soda/sodium bicarbonate... If you're putting the Kalk in too much, too fast, and there is insufficient carbon dioxide to neutralize the hydroxide (the OH- of the Ca(OH)2) of the Kalk... you are going to be precipitating out your calcium, magnesium, strontium... with the addition of "alkaline buffering" materials.... Does this make sense to you? Bob Fenner

pH problems Dear Robert ( Bob ) Fenner, I am most delighted to know that you can help us on problems with aquarium. I hope you could kindly assist me to resolve my question below:- <I will try> The PH of my marine tank ( containing Live-rock, 5 Anemones, Hard and soft Corals and 2 nos Crown Fish )is usually 7.7 and when added with Seachem PH 8.3 ( Raise and maintain pH to 8.3 ), the pH raises to 8.6.immediately but will gradually drop to 7.7. Question #01 : How do I maintain the pH to be 8.2 constant. <There are a few "stock" ways... the addition of a product (buffer, alkaline booster) as you mention, added soluble carbonates, bicarbonates from rock, substrate, adding oxidizing influences (e.g. aeration, photosynthetic organisms, ozone...), alternatively removing reductive influences like overfeeding, overstocking...> Question #02 : What affects the changes of pH in marine tank and why do it always drop to 7.7. <Point at which the systems buffers are "set"... where there is sufficient resistance to further dropping (up to a point)... Do you understand the relationship between pH and alkalinity? Please read: http://www.wetwebmedia.com/marphalk.htm> Question #03 : What do Box Fish ( Coffin Fish - small species ) feeds on or what substitute can I feed with. I have tried blind shrimp and invert min but were rejected. <Please read the areas on Puffers and beyond: http://www.wetwebmedia.com/puffers.htm You need to experiment with other meaty foods, live rock> I would most appreciated if you could kindly assist me in resolving these problems. Thank you in advance. <You're welcome my friend. Bob Fenner> Jun Margaret

NO3 Test Kit and PH Buffer Hi Bob, I have a reef tank of about 180 gal and have been using Tetra's test kit for NO3 for some time. Recently I bought an API NO3 test kit and discovered a big difference in the test results. Very roughly, the Tetra test kit gives a result that is 4 to 5 times higher than the API one. Bob, are you aware of such a difference and why? How should I interpret these readings? <Mmm, there shouldn't be such a large difference as this... Do check for me if the "units of measure" are the same... "Nitrogen as Nitrate", Nitrate in ppm, what have you... and take a sample of your water to a local fish store and have them check your NO3 level... it may be that the reagents of one kit have "gone bad"> I have been using Ca Reactor for my reef tank since 2 months ago. Over the past 2 months, PH dropped from 8.5 to 8.1. It has stayed at this level (8.1) for the past 2 or 3 weeks. My KH is about 10 or 11. I am wondering whether I have added too much CO2 and is trying to reduce the amount.  <Hmm... the pH and KH levels are fine... you might experiment with letting the effluent pH (from the calcium reactor) be a couple of tenths of a pH point higher... and see what this results in pH and alkalinity wise over a few days...> My question is: would the use of Ca Reactor, with the right amount of CO2, be able to maintain a stable PH of around 8.2. <... yes... given one more principal factor... the type, amount of "feeder stock" that you're melting in the reactor> I also understand baking soda can be used to maintain the PH, but not sure whether I should go for this option together with the use of Ca Reactor. Your advise is much appreciated. Regards, David <Baking soda, sodium bicarbonate won't raise the pH in settings, levels of use in a situation like yours... you could add some calcium hydroxide solution (Kalkwasser), calcium chloride... but I wouldn't, am not concerned... a pH of 8.1 is fine. Bob Fenner>

Re: NO3 Test Kit and PH Buffer Thanks Bob for your very prompt reply. Both the Tetra and API test kits say they measure nitrate (NO3-) in ppm or mg/l. <Yes... these are equivalents> In particular, API says it measures total nitrate which may be 4.4 times higher than some other kits that only measure Nitrogen as Nitrate.  <This is so> But in my case, I got higher results from Tetra which does not seem to make sense to me.  <Simple stoichiometrics my friend... you can/could do the math... nitrogen as a percent of nitrate... three oxygens to one N...> I had in fact tried 2 different samples from different sources, one from my tank and one from tape water. The Tetra gave a reading of 20 ppm for tape water and 40 ppm for my tank. The API gave a reading of 4 ppm and 8 ppm respectively. <I believe both...> On the pH problem, I am not concerned about a 8.1 pH. However, since I noticed the drop in pH, I was anticipating a further drop and therefore planning ahead of what to do in case it drops below 8.0.  <Mmm... good to anticipate, plan... but you may never experience this "drop" due to sufficient alkaline reserve at or about the 8 or so point> I read somewhere in your website about an opinion that if nothing is done to maintain your tank's pH, you would expect the pH to drop by 0.1 every week and adding baking soda is a solution to this pH depletion problem.  <One solution, yes... as are water changes, ready-soluble sources of carbonate, bicarbonate in a system...> Just to make sure I get it right, is it true that the use of ca reactor, in a proper manner, should by itself alone, take care of the pH depletion problem?  <Yes... as well as biomineral, alkaline content, carbon dioxide availability...> And if one has to raise the pH level, calcium hydroxide (or calcium chloride) should be added, rather than baking soda? <At some point, yes... In most systems, the addition of sodium bicarbonate will not elevate pH beyond about 7.8... try it yourself...dissolve some in freshwater or some freshly made and pH depressed (maybe with the simple organic acid acetic, or vinegar, CH3COOH) seawater...> Am I also correct to say that adding baking soda will maintain or increase the buffer but not the pH? <... Mmm, yes... the baking soda will only increase the pH to a point... but will continue to add (to saturation) to alkaline reserve... at that point> I am somewhat confused about a high pH and a high buffer. Is it correct to say the two have no direct relationship, but a high buffer will help to maintain a constant pH (whatever it is, high or low)?  <Yes... you do understand> Once again, I thank you for your help, this is my third time receiving advices from you. Regards, David <We will keep going over these phenomena, pH and alkalinity, till you feel you understand them. One is a "point", the other "resistance" to change in that point. Bob Fenner>

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