I disagree that you should never
adjust the pH. If you have tap water with very low KH/buffering (like I do) then you will get drastic pH swings that will quickly kill off fish. In cases like mine I have to stabilize the pH. Out of tap it's around 7.6 - 8.0; within 24 hours it's at 6.0 or below. I never use pH up or down though, because the pH level isn't what is important... pH stability is what really matters. Seachem makes two excellent products which I have had great success with: Neutral Regulator and Gold Buffer.