[will5]

So how much of an affect does this pH swing that Co2 causes have on the fish?

I have heard that some people run CO2 24/7 but how is this done with out killing the fish?

 

[rich815]

None. It's only about a point or less and it's gradual.

 

[Hoppy]

I agree with rich815. Most people running high CO2 levels shut off the CO2 when the lights are off, but I have yet to read or hear that someone had problems with their fish as a result.

 

[MarkMc]

It seems (by personal observation) that a gradual ph swing due to CO2 injection has little to no apparent detrimental effect on fish. I'm talking a point or less ph drop. I have neons and bleeding heart tetras that are over 2 years old and are very healthy that have lived everyday of their lives with a daily ph swing. I also believe that fish need a gradual adjustment period to CO2 injected water. If you introduce new fish to your tank during the later part of the light/CO2 cycle they can show signs of stress.If you acclimate them before the lights and CO2 comes on they will show no stress later when the 1 point drop has occurred. Again, these are just observations and not based on any study, so it's possible that there is something impacting the health of fish in these CO2 on/lights on ~ CO2 off /lights off setups but you sure can't tell by the fishes appearance.