True, when I read my post back, I should have mentioned that CC raises it, not lowers it. I was giving examples of natural products.
Mr. Limpet has a good point with the peat moss, its a good option to lower it, but personally I'd find fish that suit the water, not water that suites the fish.
For easy math, if the pH in the tank was 6, and out of the tap was 8...if you did a 50% pwc it'd be an instant 1 point swing before the peat moss has a chance to alter it. That sudden fluctuation can be stressful.
You can make it work one way or the other, I actually run a tiny bit of CC because my water is ridiculously soft and has no alkalinity, is just go the easier route.