ADA Aqua Soil and CO2 Injection

Dangerous pH levels for the fish are lower than I suspect you think. As long as you are lowering the pH with CO2, and not by adding muriatic acid or other acids, the fish aren't going to be bothered by some pretty low pH's. But, adding too much CO2 will bother the fish by suffocating them. pH just isn't as critical a parameter for them as most of us used to think it was, but total dissolved solids is probably more critical than once thought. That's why changing 80-90% of the tank water with tap water doesn't normally bother the fish at all, even though the pH will likely change quite a bit while doing that, but adding a big measure of bicarbonate of soda to raise the KH will bother the fish. At least, that is how I am interpreting what I have been reading here and on other forums.

 

I have a KH of 1 out of the tap, and I am in the process of switching from eco to ADA AS as well. I know my KH will drop to zero as a result, and my present pH of 5.9 with CO2 injection will probably have to drop to 5.3....does that bother me? no...will it bother my fish? no. The only thing I keep an eye on with this type of drop is I make sure that I have enough agitation in my water column to provide fish with O2. That is it. Co2 doesn't hurt fish as much as lack of O2 does. As it is now, my pH fluctuates overnight because I turn off my CO2 when the lights go out. My fish have never shown any sign of sensitivity to this delta...I even have the same original 10 otos I started this tank with, and they are considered sensitive, I hear.