# HOw do i introduce co2 into a community aquarium



## colonel mustard (Apr 21, 2007)

I would like to put co2 into my tank but i have read that sudden rise in co2 levels and drop in oxygen levels can kill fish inhabiting the tank. I thought that mabey by making more ripples on the water's surface may drive off some co2 so that i can then slowly reduce the amount of water disturbence until i have 30ppm and healthy fish. but is this practical never mind possible?

thanks for any replies


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## Bert H (Mar 2, 2004)

If you have sensitive fish, I would start slowly. I have guppies and went directly to 25+ppm in one day without problems. You need to know your water chemistry, as in kh to know whether to expect a quick drop or a slower one once you start the CO2. Get a good pH and kh kit to accurately measure these parameters. Then start your injection slowly. I don't see any reason why most fish wouldn't be able to handle a CO2 level of 10-15ppm. You can build up then to your target, assuming it's 30ppm. 

The above all assumes you have pressurized, because with diy, you have very little control over flow rates and output of CO2. With pressurized, you can also go with a solenoid to turn it off at lights out, or inject some air into the tank at dark times if you feel your fish are stressed. 

My 2 cents.


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## evercl92 (Aug 14, 2006)

colonel mustard said:


> i have read that sudden rise in co2 levels and drop in oxygen levels can kill fish inhabiting the tank.


This may be true, but be aware that CO2 does not displace O2 - increasing CO2 levels doesn't necessarily mean that O2 levels will decrease. Actually, given enough plant mass, O2 levels will increase as the CO2 increases due to the plants respiring.

You should still test to find out what your pH and KH values are. You don't want to induce a huge pH swing by injecting CO2 and by having a low KH.


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## colonel mustard (Apr 21, 2007)

so the more kh the less large ph swings?


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## hoppycalif (Apr 7, 2005)

The change in pH for a given amount of CO2 being dissolved into the water is the same no matter what the KH is. If you dissolve 30 ppm of CO2 into water which started out with only 3 ppm of CO2 in it, the pH will drop by 1.0 whether the KH is 1 or 10 or anywhere in between. The only thing the KH affects is the actual value of the pH at a given ppm of CO2.

Unless you have a very small aquarium and a very high bubble rate you can't quickly raise the ppm of CO2 in the water. For a typical 50 gallon or so aquarium with a typical external reactor and typical canister filter it is going to take an hour or more to reach the final ppm of CO2 for a given bubble rate. But, if the fish have not been in high CO2 water before they will likely be more distressed by high CO2 ppms than will fish who are used to it. So, you could try slightly increasing the bubble rate each day until you finally get to the ppm you want. That is a pretty good idea anyway, because a drop checker, which is the only accurate way to measure the CO2 in the water, reacts so slowly you risk overshooting your goal if you try to go more rapidly.


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## Bert H (Mar 2, 2004)

colonel mustard said:


> so the more kh the less large ph swings?


Not exactly. From personal experience, it takes longer to drop the pH (subsequently increasing CO2 concentration) when you have hard (high kh) water than when you have soft (low kh) water. In my tanks I found if I run the CO2 on a solenoid, it takes too long to achieve the 30 ppm, so I just leave it on 24/7 now.

As Hoppy said, 30ppm of CO2 will drop your pH 1.0unit no matter what your kh is.


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## hoppycalif (Apr 7, 2005)

Bert H said:


> Not exactly. From personal experience, it takes longer to drop the pH (subsequently increasing CO2 concentration) when you have hard (high kh) water than when you have soft (low kh) water. In my tanks I found if I run the CO2 on a solenoid, it takes too long to achieve the 30 ppm, so I just leave it on 24/7 now.
> 
> As Hoppy said, 30ppm of CO2 will drop your pH 1.0unit no matter what your kh is.


I have been running my CO2 24/7 for the past month, but my CO2 ran out pretty quickly that way. So, it occurred to me that since my lights are only on for 8 hours, I can start the CO2 flowing 4 hours before the lights come on and that will cut my CO2 usage in half. That is what I'm starting to do now.

Oh, and 30 ppm doesn't necessarily drop the pH by 1.0. An accurate statement is that a pH drop of 1.0 means the amount of CO2 in the water went up by a factor of ten. So, only if it started at 3 ppm will it end up at 30 ppm.


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