Stability is the key for the fish. They adapt just fine. But if you decide you want to make a small change, add a large piece of Malaysian Driftwood. I had 2 pieces in my 55G, currently only 1, and my ph hovers about .5-.6 less than my tap water after sitting out 24 hours. It won't lower it immediately, it gradually lowered over about a month before it stabalized. My tap is 7.8, and my tank sits at 7.2-7.4. Other than that, I would not use any chemicals in the tank. And I personally don't like using RO water, because then you have to make sure you get the correct mixture before doing your PWC. So for my opinion, either leave it, the fish will be fine, or add driftwood, will lower the ph a little bit naturally.