I read about a similar problem somewhere on this site. I think it has to do with kH or hard water, can't remember which one. Anyway, which ever it is, if it is off then no matter how much you adjust your pH, it will always return to what it was before. But I agree with L.M.K. on maintaining a stable pH. Here is my reasoning: If you look up the "stats" on any fish they will usually give the pH of its natural habitat. But most of the fish at LFS are tank raised. How do they know what their "natural" pH is supposed to be? The pH from my tap is a little under 8, and I never mess with it. My central and south american cichlids have been doing fine the last 3 months since I set it up.