Don't use chemicals to mess with your pH. Seriously you are looking at a recipe for disaster on that. You are better off to have consistent parameters. If it is really important to do it, you would be better off mixing your water with RO
water. But either way stability is the more important than the perfect pH. I have liquid rock for water and my pH is always high. Most likely you will want to choose fish that prefer harder higher pH waters like african cichlids or mollies.