Is nightime the right time for CO2? - The Planted Tank Forum
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post #1 of 4 (permalink) Old 01-12-2009, 06:13 PM Thread Starter
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Is nightime the right time for CO2?

I am just so confused.

I am being encouraged on the one side (by no less a person than Tom Barr) to run an airstone in my tank at night to keep up the O2 levels when the plants quit contributing.

My LFS guy (Dan at HAW, Houstonites, myself included, really respect his opinion) says I should run my CO2 all night because it takes so long for the CO2 to diffuse all thru the tank in the morning when the lights come on.

Of course, there is not a lot of point in adding CO2 if you are just going to drive it off by agitating the water with an air stone. (Okay O2 does not drive out CO2, but an airstone does drive it out, just by agitating the water).

I am thinking about about changing my "manual" pressurized CO2 system into an "automatic" one (though I am worried about keeping the pH controller calibrated, a topic for another thread), but I think if you tried to maintain a constant pH with an airstone running you are going to run thru an awful lot of gas.

What is the best schedule for airstones, lights, and CO2?

What if I were to turn the the airstone on and the CO2 off when the lights went off, then turn the airstone off and the CO2 on, 4 or 5 hours before the lights come on?

I would be vulnerable to low oxygen levels just before lights on, but if I time it right I should be able to have some CO2 built up by the time the plants need it but still have some oxygen left in the tank.

Does anybody use a schedule like this?

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post #2 of 4 (permalink) Old 01-12-2009, 06:33 PM
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Are the fish gasping for air? If they aren't then they should have plenty of 02. Myself, I just put a regular three prong timer on the solenoid for the C02 to go off with the lights (give or take a couple of minutes) and to come back on with the lights (maybe half an hour or so before the lights come on). Haven't had any problems with C02 or 02 on this schedule. I run about two bubbles per second or so on my 55 gal. and 1 bubble per second on my 29 gal. No gasping or problems. I run no airstones at all.
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post #3 of 4 (permalink) Old 01-12-2009, 06:49 PM
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CO2 builds up in the water in an hour, so there is no reason to keep it on all night. (I'm assuming a pressurized CO2 system, of course.) CO2 at night is of no benefit to either fish or plants, so there is no good reason to keep it on at night. If you use a drop checker to determine that you have enough CO2 in the water, it does take 2 or more hours for that device to stabilize and give a usable reading, but the CO2 is in the water much quicker.

Tom Barr turns his CO2 on and off with the lights, and it works fine for him, even with a 180 gallon tank. Those of us with less efficient means for dissolving the CO2 in the water might do better by turning it on an hour or less before the lights come on, but I'm not even sure that is a great idea, even though I do it. I do think that turning the CO2 off before the lights go off is a good idea, when you use an external CO2 reactor, because there will be residual CO2 in the reactor for some time after the solenoid goes off.

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post #4 of 4 (permalink) Old 01-12-2009, 08:31 PM
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Why start another thread on the same subject that you've already got in
progress? I believe all the answers you seek are already there.


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