Hello Marcus,

If your tank has many plants in it and is not overstocked with fish
just put your air pump on a timer and run it @ night only.
Be sure to watch the fish the ist day for sign and sypmtoms of o2
depravation but generally they will be fine

My tank is rather well stocked, with about 45 fish for 40 gallons (at times
it can contain a few more). But almost all of them are quite small,
including 15-20 neon tetras. Only the two pearl gouramis are on the larger
side. And I do have lots of plants. Still, while my tank isn't ridiculously
overpopulated, I think your advice of having the air pump run during the
night is a very good idea. Since plants don't do photosynthesis during the
night, they don't need the CO2 anyway.

The first time I tried turning off the air pump while using the CO2
canisters it was off for 16 hours. I noticed that some of the fish were
breathing faster, though they weren't going to the surface. But they don't
seem to mind 12 hours. A 12/12 cycle might be good for the air pump. The
plants just won't get as much CO2 for a few hours during the bright period.
Seems like a good compromise to me.

Thank you very much for the advice.

Francois