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How many CO2 bubbles per gallon of water?

80776 Views 45 Replies 13 Participants Last post by  Skelley
I just setup my DIY CO2 system using soda bottles... I have no clue if the CO2 I am inyecting is to much or to little.

I have a 20 gallon tank.

Is there anyway to aproximate the required number of bubbles that need to go in the tank (assuming 100% disolution) to reach an acceptable CO2 level?

I am currently getting a bubble every 3 to 4 seconds.... does that seem right?
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Yes you need a test kit to measure KH, or you can ask your LFS to test your water and tell you what it is. I'm not too sure I would follow their advice about it being too hard.
Does KH stand for anything?, they tested it for Chlorine, Nitrate, Amonia, Hardness, and PH yesterday.
There are two types of hardness, GH-general hardness, and KH-carbonate hardness. KH is what you want for determining how much CO2 you have. Get them to test your KH, they should be able to. Once you know your KH and pH you can use the chart to determine your CO2 content. I use Hagen test kits. They use color charts so you cant get it perfect, but I can get pretty close. They are pretty cheap too.
Ph rising rather than lowering...

I do not have the test kit for KH yet, but my Ph is rising!! I measured it this morning (which supposedly since there is no light at night should be the lowest number of the day) at 7.2 (using color charts, aquarium farmaceuticals kit) what is happening!?
Do you run your co2 at night? If not then your ph could rise overnight.
I left it running all night.
I don't use bubble rates to set my CO2 to nice levels.
I maintain my KH at 4 and then increase CO2 steadily until I get a pH of 6.7 to get 24ppm of CO2.

You can maintain a good stable KH with additional calcareous filter media (coral chips, limestone, etc) or by adding CaCO3 every water change.

CO2 and lights are 10hours a day. At night I aerate the water for 14hours to provide O2 for the increased demand. Something I learned from some ADA publication.
If you do decide to airate your tank overnight, make sure you test your PH first thing in the morning prior to the turning off the air pump. In many tanks, plant uptake contributes to a small percentage of overall CO2 loss/consumption. Gas exchange actually accounts for most of the CO2 loss in a tank. Therefore, not everyone needs to aerate at night, actually for many, this would cause a bigger PH swing than leaving the CO2 running all the time.

Hope that helps
Giancarlo Podio
My pH does swing but it doesn't affect my plant and fish health.
My tank woke up to a 6.7-6.8 ph at 7:00 this morning, right before turning on the lights.

Good thing you touched on the Ph swing subject as that was going to be my next question.

I have read a lot that fish do not like Ph swings, but how much is too much... unless you have aPh controller (and maybe even then) there will be Ph swings... photosintesis ocurrs at daytime only, hence my CO2 concentration is bound to be higher at night...

What is the general concensus on leaving CO2 on at night or not? Other than CO2 how can one reduce Ph swings to a minimmum or at least to a level when it will not affect fish?
The pH swing is of no occurs in nature as well and more rapidly then what we experience in our tanks. The issue here is whether there is a need to aerate in the first place? When plants are growing well, they saturate the entire water column with loads of O2 far more than any number of airpumps or powerheads can get in. Unless you are seeing fish discomfort in the morning due to lack of O2 (too much critters), you are just wasting away the O2 buildup by plants.
I've never required air pumps for O2 levels and feel surface agitation is enough for most setups. The reason why some use pumps during the night is to avoid CO2 levels from becoming too high and possibly becoming dangerous. Although PH in nature will vary from rainfalls and changes in seasons, we are comparing it to a daily change from day to night, this may not be as "healthy" as nature's way of doing things. If your PH changes more than 0.4 between day and night, you could do a little better. If your fish don't seem bothered by your current setup, then don't change anything, they are probably used to it by now.

Due to the high CO2 levels I keep and low surface agitation, I have my CO2 powered diffuser connected to the light timer, this has proven to be the most stable in this tank, if it had more surface agitation I'd probably leave it on 24/7 but wouldn't be able to bring CO2 levels as high as I do now during the day.

It's all about balancing CO2 loss and diffusion rate, plant uptake plays a small part for tanks with moderate surface agitation/gas exchange levels.

Hope that helps
Giancarlo Podio
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OK, just got my KH kit...

I am measuring P = 6.8, Kh = 8 -> CO2=38.

I was told to shoot for CO2 between 20 and 30, so I know this level mey be a bit high...

When you talk about dangerous CO2 levels... what range are you talking about? Is CO2 dangerous to plant, fish or both, at what levels?
CO2 can be dangerous to fish at extremely high levels. 38ppm should be fine, although a little high I believe. Try this site for great CO2 info: Pressure CO2
I have had co2 levels much higher than that and never had a problem. At time when I was fiddling wihtt he CO2 setup, or for other reasons, and the fish never seemed to mind. I at one point had had 11 neons, 2 golden barbs, and 2 otos in a 10 gal wiht tons of plants. I accidently hit 90ppm of co2 a couple of times. I know this lasted for several hours and the fish were not gasping or even acting funny. I do not recomend trying this and mine was an accident dut I generally have it int he 35ppm range adn no one cares. I only have 7 neons in there now, not because of deaths though:) My plants seem fine adn this is an easy number to stay at based on my water and co2 setup. I believe that part of hte reason mine can get so high wihtout any ill effects is the fact that my plants (and I have a lot) producea lot of o2 during the day. I am sure that even witht e high co2 levels that there is planty of o2 in the water, even after all night. For instance this morning I had 60ppm of co2 because I just changed my mix and it was not fine tuned yet. My fish are fine but my plants also produce fairly steady streams of o2 through out the day. One thing to remember is that co2 saturation in the water does not force out o2. At he end of the day, if your plants are growing well, your water will be highly saturated with both CO2 and O2.

ANyway, I ramble so hope this helps.
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Does it matter, from how deep the bubbles leaves the tank? For better diffusion is this important?

And, if I make a diffuser, so the CO2 stays in the water longer, does diffusers deepness makes any diffrence in efficiancy?
Hasan, the placement of your diffuser near the bottom of the tank is best.

You want the CO2 bubbles to be in contact with the water as long as possible. The bubble will dissolve into the water as it floats up. Placing the diffuser at the bottom will keep the CO2 bubble in contact with the water longer for maximum CO2 dissolution.

-John N.
Thanks for the fast reply,

I have made my own diffuser from an old music cassete case. Im using the part that looks like a U shape. When turned upside down, the CO2 fills in it. CO2 being stable in the diffuser, does it still diffuse at maximum?
Sounds like you have a CO2 bell contraption.

If the big bubble is staying inside the cassette area, and not releasing any gas to the surface, Then you have a great diffusion method, and the rate it diffuses at is the same as the output. You are getting good co2 diffusion.

Test your pH and KH to see how much CO2 diffusion you are actually getting in ppms, compare it to the charts in the Fert section. You'll be looking for a drop in pH when adding CO2 compared to straight from the sink.

-John N.
Well, it seems Im not getting any diffusion..:( I had to turn off the CO2 supply off, (becuse of a technical problem but it will be back working tomorrow) I realised that the CO2 in my diffuser isnt decreasing, it seems that its staying in the water and not diffusing.

Also, my pH seems to rise...that is odd, my tap water is 6.8 whereas my tank water which is from the tap, yesterday was 7.2, today 7.3. This rise may be of the CO2 supply turned off.
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