Stability of ph is often much more important than the "perfect" ph. Of course, if your fish require very basic water and your tap is very acidic... it may be a different story, imho. In addition to my question about why you are interested in raising the ph, what is your stock and what is your tap's ph?
Please correct me if I am wrong...however I am curious if you know your KH (Carbonate Hardness). If that value is high would he not have a difficult time maintaining any pH? I have the same problem with my pH. However I have too large a bio load to boot so that explains some of it. However I have a 2dh KH reading and just don't know if that is indeed low. I do think its borderline, but every week my pH has dropped from about 7.6 to anywhere from 6.6-7.0. My thoughts for this tank is to add a small amount of cc to my filter media. Does that sound right?
Adding an acid buffer may reduce the pH some, but the most effective route would be to use some distilled, r/o, or rainwater when doing water changes. Just a small percentage, but the % is something you'd have to figure out based on your test readings.