a pH of 8 would still be fine for many types of hard water fish. So the question back to you is, what fish are you keeping? If you're keeping Malawi cichlids, they'd thank you for that pH. If you're keeping Tanganyikan cichlids, they'd be hoping you push the pH up to 9. If you're keeping discus or Rams, they'd be very unhappy with you.

pH will gradually drop over time in an aquarium once the carbonate hardness (kH) is used up. There are things like "pH down" to lower pH, but usually I don't suggest you use these chemicals. Another way to lower pH would be to mix some deionised or Reverse Osmosis water into you fish tank (ie 50% tap, 50% RO water.).

If your tap water comes out with a pH above 8, and the fish you keep aren't critical about pH, I suggest you just leave it at that. It's too much hassle tinkering with chemicals and pH. In most cases, pH is the least of your worries. Worry about ammonia and nitrite b4 your pH.