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.