I have very hard/alkaline tap water as well, around pH 7.8, dGH 9, unfortunately I like mostly fish who enjoy soft, acidic water! So I have done a lot of experimenting with water.
As discus said, most fish will adapt, however some species are more sensitive. While you may not be trying to breed fish who like acidic water, most species that come from acidic waters will definitely enjoy a lower pH/GH and will show a lot more color. For example, my Rasbora espei first spawned in pH 7.8, but now I regularly breed them in pH 6.4, and they are way more colorful and much more prolific.
Basically if you want to lower the pH, you need RO as markopolo said. You can add pH buffer all day long to your tap water but the pH will just go back up due to the hardness.
Personally I use a simple RO unit from eBay ($100 roughly) and then add a little bit of Seachem buffer powder, and by a little I mean like a pinch per gallon. This will prevent large pH fluctuations. This will get you really nice, soft water for pretty cheap. You can get the Seachem pH regulator at PetSmart for $10, and it will last you forever.
If you want to monkey with RO, go to your local supermarkets and find one that has a drinking water dispenser... Usually those are actually RO, here it's about $0.39 a gallon.