furballi

A concentration of +90 ppm can be lethal to fish. It is impossilble to elevate the CO2 level to this lethal concentration if you dial-in 15 to 20 ppm of CO2 as the target range. Again, the key to any CO2 injection rig is the needle valve.

Don't believe those people with pie-in-the-sky "what-if". These people have very little understanding of physics and will come up with BS cases to make their point. None of these "what-ifs" can be supported by controlled scientific experiments.

gf225

I now run 24/7 CO2 mist with plenty of circulation and surface movement to ensure O2 at night.

CO2 is cheap enough.

I also found my glass diffuser prone to blocking with it off at night (limescale build-up I think).

Pinto

i turn mines off same time as light. Thinking of keeping it on because of growing algae problems

hoppycalif

One advantage of CO2 mist is that you don't need to have all of the CO2 in solution in the water, so you can have a lower ppm dissolved in the water. The plants will get much of the needed CO2 from the tiny bubbles, instead. That would let you safely run the CO2 24 hours a day without worrying about the effect on the fish. And, the hidden advantage is that to make the mist system work at all you need very good water circulation all over the tank, so you get the maximum effect from all of the CO2.