Co2 Duration Question

Some people leave it on when they aren't putting in large amounts because they figure that CO2 doesn't shut off in the wild, so why in a tank? There really isn't any benefits to it. Just less work. They have to also watch their pH though, because unused CO2 can cause changes in the pH which wouldn't be good.

I would recommend turning it off because, even though it is a little bit more effort, you avoid risks and save more CO2 in the end, which could save you some money.

in densely planted tanks respiration of plants during the night is enough to maintain co2 levels high and your system will not need to inject any if on a controller.In tanks with only a few plants in the ph will rise at night if the co2 is shut off and I don't this swing is good for the fish.I don't know though if some swing occurs in nature during the night.

The reason people turn off the CO2 at night is because they have an uncontrolled input of CO2. Since plants do not use CO2 at night, the amount of CO2 dissolved in your water can reach excessively high values and be bad for fish.

If you have a CO2 controller, it doesn’t matter whether you leave the CO2 on or off.

BTW The level of CO2 in a typical planted aquarium using pressurized CO2 is about 50 -100 times the normal level found in nature.