Is it appropriate to turn of CO2 at night?

kevmo911 said:

I may be mistaken here, but as long as the fish don't start gasping for O2, they should be fine, and that running CO2 at night will increase the CO2 water saturation, so when the lights come on and plants start to absorb the CO2, that extra CO2 in the water column will do the plants good.

Meaning, as long as the fish don't appear to suffer, running CO2 overnight is not only not bad, but would be better for the plants than not running it?

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This is very ambiguous, though. It really depends on the rate in which CO2 is entering the tank and seeping out through the surface - only with that info can you determine what the levels might be.

For example, say I run a high rate of CO2 during the day and the fish are fine as long as I turn it off at night to let it off gass for a while. Perhaps if I didn't turn it off at night, the CO2 would slowly build and gas the first.

Or,like you said I could run the CO2 so perfectly that the CO2 could run all night, slowly building CO2 concentration to the exact amount that would be used by the plants during the next day. It seems tricky to get this equilibrium, though.

To me, it seems wisest to turn on the CO2 before the lights come on and turn it off when they go off. That way, you use less CO2 and the tank has more time to let CO2 out to avoid gassing the first. An airstone would further ensure that the CO2 levels would go to ambient levels during the night.

But, is there a concern with either ph swinging from the on/off/airstone cycle? Any other concerns?

Thanks for the responses everyone. You are helping me a lot.

I am also concerned with ph level fluctuations. I am not sure how one stabilizes pH when it comes to lights on or off and CO2 on and off.

I think I can figure out an easy solution to decrease the levels of CO2 in my tanks at night and not losing pressure in my DIY 2 liter CO2 bottles.

I have the Tom's Dive Clean 85-1 filters. There is a nozzle right above the flow exhaust. It is made to attach tubing and to allow the tubing to be placed above and outside the tank. This creates an effect like an air stone. I thought I could have this attached but capped closed during the day and then open it while the lights are off. It is more powerful than an air stone and creates a ton of air bubbles. The only drawback is that I would always have to manually open them up every night and close them during the day.

I guess it would be easier to buy an air pump and run air stones in each tank on one timer. It is just that I made a DIY hood light with two under cabinet T8 lamps per tank so that is 10 plugs right there. Then I have five heaters (which hardly ever go on because the lights create water temperatures of around 84 degrees - I have the heaters set at 81), and lastly the five filters going. So that is 20 plug ins. I guess, for stability's sake I can throw in an air pump and run it with multiple valves and disperse it over five tanks.

Bubble the CO2 into a small power head during he day, connect the powerhead to the light timer, when the lights are off, the bubbles simply escape, no CO2 added to the water.

Very simple solution.

Make sure to prevent the brew from being sucked into the impeller/powqerhead due to positive suction, leave a 2" or so gap btw the CO2 bubbling in, and the suction side of the powerhead.

PowerHead

Then 2" below

DIY CO2 source

Regards,
Tom Barr