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FAQs on Carbon Dioxide and Planted Tanks: Compressed Gas Types

Related Articles: Carbon dioxide and the planted freshwater aquarium by Neale Monks, CO2 Canopies,

Related FAQs: CO2 & Planted Tanks 1, CO2 & Planted Tanks 2, CO2 Canopies, & FAQs on CO2 Planted Tanks: Rationale/Use, Sources, Yeast-Bottle Types, Control/Delivery, Measure, Dangers,

Large Planted Tank with CO2 9/19/10
I have started a 150 gallon planted freshwater tank and have a previous CO2 system I would like to add. My dilemma is 1) how do I measure how much CO2 I need for such a large tank? 2) I have a small ceramic glass diffuser from ADA that is about 1" diameter. It says it is for up to 20 gallons which is too small for my tank. What do I need to use as a diffuser for such a large size tank? I have upgraded to a used 0.6 kg CO2 tank (please see picture) and had it modified to attach to a simple CO2 system bought in a local pet store. I have a glass bubble counter to suction to the outside of the tank and a glass CO2 reader which shows yellow, green, or blue depending on how much is in the water. Should I just put the diffuser in there under the output tubes and see what the CO2 reader says in a day or two? I have attached pics of when It was hooked up to my 20 gallon quarantine tank I was using for plants. I have invested too much money in this already and am not really looking to add to it if I don't absolutely have to. Is there any way I can use this system in my large tank?
Thank you all!
<Lisa, having seen photos of your tank, I'm almost 100% sure that CO2 will make no difference at all. Can I strongly urge you to focus on [a] light intensity and [b] choosing the right plants for your ambient lighting levels, water chemistry, water temperature, and water current. I have an article about all of this coming in the next WWM Digital magazine which should be up in the next week. But in brief, there are two ways to decide how much CO2 to add. The first is trial-and-error. Assuming intense lighting, if you add CO2 at the tiniest amount you can in bubbles/second and wait for an hour, you should see "pearling" of oxygen bubbles on some plants. If not, add a tiny bit more. Repeat as required, all the time checking that [a] the fish don't look stressed and [b] there isn't a wild pH swing (there will be a slight pH decrease as you add CO2, but if it goes from 8 to 6 that's too much!). This approach is hit-and-miss and not terribly safe. The better approach is to use a CO2 test kit to measure the dissolved CO2. This should be between 10 and 20 mg/l. Add sufficient CO2 for a concentration of 10 mg/l, wait a couple of weeks, and if plant growth still isn't as good as you'd like, increase to 15 mg/l, and then a couple weeks later to 20 mg/l if needs be. Again, make sure the fish stay happy.
Above 25 mg/l CO2 will quickly kill your fish; in fact using CO2 is quite a good way to euthanise fish! So be very careful. There is a relationship between pH and CO2 concentration assuming you know the carbonate (not general!) hardness, so you can use a pH test kit to measure CO2 concentration. The formula is 3 x carbonate hardness (in degrees KH) x10(7-pH); thus if carbonate hardness is 5 degrees KH and the pH is 7.6, then the amount of carbon dioxide in the water will be 3.78 mg/l. If you're maths-phobic, then using a CO2 test kit will be safer. With all this said, your aquarium doesn't have enough lighting for CO2 to make much difference either way. You'd get far better results concentrating on plants adapted to relatively low light levels. These will find the CO2 produced by your fish and the filter more than enough, and even more so if you added a proper substrate, since microbes in the gravel and sand produce CO2 as well. Anubias, Java fern, Cryptocoryne wendtii, Vallisneria spiralis, hybrid Aponogeton, floating Indian fern, Amazon Frogbit -- all these should do fine in an aquarium with 1-2 watts/gallon, without the need for CO2. There is a VERY COMMON misconception in the hobby that CO2 is the thing that makes or breaks plant growth in aquaria. To some degree, the people selling CO2 appliances foster this idea. But it is COMPLETELY WRONG. While CO2 can make good planted tanks even better, it won't turn around a poor or mediocre one. It's a bolt-on goody for already successful systems. Cheers, Neale.>

CO2 in planted tanks 9/22/08
I have a question regarding CO2 levels in a planted aquarium.
First I'll start by telling you about my setup and my problem. I have a 20L planted aquarium.
<Do you really mean twenty litres? That's a bucket! Or is this a "20 gallon" tank in a long format?>
Plants include Ceratopteris thalictroides, Nymphaea zenkeri , Lilaeopsis brasiliensis, Hygrophila difformis, Hygrophila corymbosa, Echinodorus ozelot -- one of my favorite plants, grows like a weed, Hydrocotyle leucocephala, and Vesicularia dubyana. Inhabitants are 2 LF zebra Danios, 2 LF leopard Danios, 1 LF gold Danio, 1 LF blue Danio, 1 female pearl Gourami, 7 Otocinclus, 1 ghost shrimp, and 2 cherry shrimp. At one point I put a couple MTS in there to keep the substrate turned where I can't gravel vac, but I haven't seen any since.
<You won't! Melanoides be well hidden by day.>
The tank is drilled and plumbed to a 5 gallon sump. I use a Rio 1100 for the return pump, and a Visi-therm Stealth heater (can't remember wattage... 100 or 150) is in the bottom of the sump. I made a couple filter socks out of 50 micron felt for mechanical filtration, and I clean them weekly. I don't have any other filtration, I rely on plants and 5 gallon weekly water changes to take care of the bio-load. Lighting is a 2x24W T5 HO fixture, with 6700K bulbs. I have a DIY yeast CO2 system, consisting of two 2-liter bottles. I mix 2 cups sugar, 2 cups water, and 1/4 teaspoon active dry yeast into the bottles. I replace the old mixture every two weeks, and try to alternate the bottles so that I change out the first on one week, and the second on the next week. I know they're producing CO2 because they develop a nice foamy head a few hours after I mix it, and when I dump out the old mixtures they smell strongly of beer, though I've noticed that some mixtures are stronger than others. I used this website to set up my CO2 system: http://www.qsl.net/w2wdx/aquaria/diyco2.html. The only difference is that I connected it to the Red Sea CO2 Reactor 500, instead of making my own out of a powerhead. My light is on from 11 am - 9 pm every day.
<Sounds like a nice tank.>
I feed once a day, and I rotate between a flake mixture, freeze-dried daphnia, freeze-dried bloodworms, and freeze-dried Tubifex (all Hikari). The fish consume everything within a minute, and all have well-rounded bellies. I'll occasionally feed algae wafers if my tank looks bare of soft algae or the Otos don't look as plump as usual, but that is pretty rare.
I do 5 gallon water changes every week to two weeks using RO/DI water (getting that system was the best investment I ever made) reclaimed with RO Right. I usually add about 1 mL of Seachem Flourish 1-2x per week. I also had difficulties with shrimp dying immediately after molts, and the problem seemed to be resolved when I started adding about 1 mL of Kent Marine liquid calcium per week and 2 drops of Kent Marine liquid iodine per week. I test the water weekly just before doing water changes. The tank has been set up since August 19, and even though I had to put all the fish in at once a few days after setup (moving from an old tank) I never saw any spike in ammonia or nitrite. I attribute this to the large number of plants and the large mesh bag full of gravel from the old tank that I put into the new sump.
<Agreed; healthy plants will consume some ammonia straight from the water, and transferring live substrate from one tank to another will "seed" the new filter quickly.>
My parameters average as follows:
Nitrate - 15 ppm
Nitrite - 0
Ammonia - 0
pH - 7.4
KH - 2 degrees
GH - 4 degrees
Temperature - 77F
<A bit on the soft side for general fishkeeping, but provided your pH is stable through the day and between water changes, such conditions are certainly favourable for many fish. Do bear in mind many plants *do not* like soft water, notably most Vallisneria, some Cryptocoryne spp., and some Echinodorus spp. But there are numerous others. Do review the needs of each plant species you have, and check this hardness level is appropriate.>
I have measured pH at different times of the day, including early in the morning before the tank has received any light, and it's always 7.4. The KH is also always constant. According to most CO2 charts, this means that my CO2 is only about 2 ppm, which isn't nearly as high as I'd like it to be for the plants. My plants are growing, but not very quickly, and some of the slower ones are getting a fine hair algae on the leaves, as well as hard spot algae. I've also noticed some Staghorn algae here and there, but fortunately it's not growing very quickly. The only plant that really seems to be thriving is the floating water sprite -- I have to remove about a handful a week or it will shade out the other plants.
<Floating plants will usually grow rapidly if they're happy, though they do cut out light and more dangerously consume large amounts of trace elements from the water column. It's worth making the point that while floating plants are easily satisfied with liquid plant fertiliser, rooted plants hardly ever are. I didn't see anything on the substrate used here, and would caution you not to rely on liquid plant food for your rooted plants. Or put another way, I've never had success doing that, whereas when I've used a rich substrate (pond/aquatic soil plus sand/gravel) my plants have always done very well.>
I would think that two 2-liter bottles for CO2 production would be sufficient for a 20 gallon tank. I can't figure out why it's not producing more CO2.
<Theory is one thing, but if in practise you find this system isn't adequate, and you've checked its working as it should, well there you are -- case closed. While I'm all in favour of the "Estimative Index" method as a guideline for setting up and maintaining planted tanks, to some degree you can't close your eyes to the facts if the practise isn't working out. So in this case, you may need extra CO2. That said, I've never yet seen a planted tank where the absence of CO2 was stopping the plants from thriving. In my experience, CO2 makes working tanks really shine, but it doesn't turn bad tanks into good ones. So if you feel that plant growth is poor, do check other factors as well: lighting, substrate type, water chemistry. Hydrocotyle and Lilaeopsis for example need huge amounts of light to do well; to be honest even two T5 tubes are unlikely to be giving the sheer intensity of light they need. Double that number of tubes and you might be in business. You can usually tell by looking at growth: if the stems have long gaps between relatively small leaves, then there's not enough light.>
Would the fact that I inject the CO2 into the sump instead of the main tank affect results?
<Possibly; any splashing of the water has the potential to drive the CO2 out of solution.>
I try to keep surface movement as minimal as possible, but does it have to be completely still?
<Ideally, yes, but since that isn't practical in the aquarium, the best you can do is minimise turbulence.>
I can't really afford to add more bottles -- I go through a ton of sugar as it is. I also read something on this website saying that phosphate can affect CO2 readings: http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm. However, it didn't say how it would affect them -- would it give a false high or a false low?
<I don't know I'm afraid, never come across this statement before; would encourage you to contact the author directly.>
I haven't found anything else to confirm, deny, or elaborate on that statement. I can't tell what my phosphate levels are. I use the API Phosphate test kit. The scale goes from a yellow-green at 0 ppm to a blue-green at 10 ppm, and the color I get is even more yellow than the lowest number, so I don't know what that means.
<It means you have minimal phosphate; in itself no big deal as this is unlikely to be limiting if plant growth isn't fast.>
So I guess my main questions are 1) Can the presence of phosphates affect the accuracy of CO2 measurements using the pH/KH relationship, and 2) Is there anyway to improve the amount of CO2 in my tank without buying an expensive CO2 injection system?
<To answer the latter question, the electronic dosing kits are indeed very useful and worth investing in. But that said, I wouldn't drop the cash on an aquarium that wasn't already very promising. I suspect that money spent on substrate and lighting will deliver a much great bang for your buck.>
Thanks so much for reading the long email. Any help is appreciated.
<Cheers, Neale.>

CO2 Alternatives 07/20/2008 Hello....I have a 29 gal FW community tank using a Whisper 2 filter. It's illuminated with a 10K light for about 14 hrs/day. I keep the Ph at 6.8 to 7.0 and ammonia is nonexistent due to my mixing Zeolite with my charcoal filter media. <Zero ammonia should have nothing whatever to do with the Zeolite, which you shouldn't be using in a community tank anyway. Unless you have money to burn, you get much better results with biological filtration, especially at a neutral pH. My thoughts on carbon in freshwater tanks are well known here at WWM -- basically I consider it a waste of money. But again, if you don't mind spending money on stuff you don't need, by all means stick with it! If, on the other hand, you want good value and good water quality, simply through out the carbon and Zeolite, replace the space in the filter with good quality biological media (e.g., ceramic noodles) and do large, regular water changes (e.g., 50% weekly) instead.> I regularly add Seachem's Trace, Flourish, and Potassium and I place a phosphorus pad alongside my filter bag to minimize algae growth. At one time I included Seachem's Nitrogen in my additives, but that resulted in a huge algae bloom. <You shouldn't really need to add much stuff to a planted tank assuming you have a decent substrate to start with. The fish provide ample nitrate and phosphate. All you really need to add are trace elements, especially iron. Standard issue plant fertiliser will do this.> To remedy sluggish or nonexistent plant growth I installed the CarboPlus CO2 system a few years ago and the improvement is mixed, at best. <Lacklustre plant growth is almost always down to two things: firstly light intensity, and secondly substrate quality (assuming of course you've bought true aquatic plants and not terrestrial plants -- to often widely sold). You say nothing about light intensity, the 10,000K refers to the *colour* of the light, not the intensity. For standard plants, you're aiming at 2-3 watts per gallon. The actual colour of the lights couldn't matter less, as plants seem to be far more adaptable than, say, corals. CO2 is "icing on the cake" -- it makes a good system better, but it won't turn around a failing system. If you remember your high school biology, when you studied photosynthesis and limiting factors, you'll recall that CO2 is a limiting factor. Increasing light intensity speeds up photosynthesis up to a point, and then raising the CO2 concentration speeds up photosynthesis still further.> I've been considering a gas CO2 system but the tank's location gives no opportunity to hide a 5 lb. CO2 bottle. Someone suggested a yeast reactor coupled to a PGP Power Reactor CO2 system built by Plantguild Products. Does anyone have any history or comments on the effectiveness of such an approach? <Yeast reactors can work well, but they're fiddly and require careful usage. On the flip side, they're relatively cheap to run. CO2 bottles are easier but more expensive. The best systems of any kind are electronic, with automatic devices that add the right amount of CO2. If you're going to invest in upgrading an existing CO2 system, that's perhaps the most sensible approach. But if you're finding your plant growth is poor at the moment, then I seriously doubt that CO2 is the key factor, so I'd review other aspects. Are the plants suitable for your tank? Are you providing the water hardness they want? Is the water too warm or too cold? What substrate did you use? What is the intensity of the lighting? When did you last replace the lights?> As a side note, if this unit's power head is noisier than my Whisper filter, it's a no-no. Thanks for your comments! Ken <Can't really comment on this; properly build powerheads should be close to silent. If you are finding yours make excessive or rattling noises, it may be faulty/misused. Air bubbles for example make a racket when inside impellers. Cheers, Neale.>

Re: CO2 Alternatives 7/20/08 Thanks Neal....obviously you've given me a TON to think ....and rethink about. KLP <Good stuff. Keep thinking, reading, asking questions! High end planted tanks are very difficult to set up and maintain, and argue *at least* as much work as a reef tank. You want to expend your time and money as carefully as possible. Cheers, Neale.>

New fresh water tank setup 10/25/05 Hey everyone, <hello> I've been using WWM for tons of research and I finally have my first set of questions. I've been doing saltwater for about 6 months now and it's been going great. My g/f wants to get a fresh water tank for her house. I haven't done fresh water for quite some time and even then I never did plants (this will be a fully planted system). I'll just list out what I want to get and let me know if I'm on the right track. The tank is going to be a Clear-For-Life 75g and I plan on running 4x96 PC retrofit. <good> I've read actinic isn't great for freshwater so this will be all 6700 to 10000k daylight. The filtration I want to use is the Marineland Emperor 400. I don't know that I really want to go canister but if it's essential then I will. <canister provides better mechanical filtration!> The substrate is what is confusing me. I read that fluorite is hard on the stomach of Cory cats and that I should have a top layer of smoother gravel. <that is true> I've also run across floral base which seems to be less coarse. <I wouldn't worry about the Cory cats too much> Should I just stick with a 2" base of fluorite and a top layer of a different gravel? <that should be fine> What would you recommend for the top layer of gravel? <I would just go with the fluorite...the Cory cats should be fine> I imagine vacuuming will be out of the question with a full plant system but will I need to worry about any bad bacteria growing like Cyano? <not unless you have high phosphates, nitrates, etc> I'm also a little confused about the CO2 reactors. I don't want to do the DIY but I also don't have quite enough money to buy a big fully auto CO2 setup. Would something like the Hagen CO2 Natural Plant System work? Would this be enough for a 75 gallon or do I even need to worry much about CO2 with this setup? <that is only recommended up to 20 gallons...you would need something bigger than that.> <<I have used two of these units on the same tank.... will do for a larger system, if filled/maintained on a staggered basis.... I staggered mine by two weeks. Worked adequately. -SCF>> Thanks for having such a useful site and I greatly appreciate any and all advice. -Craig <good luck, IanB>

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