If you really wanted to lower your Ph, the use of driftwood (make sure you get it from a store) in your tank will slowly lower the Ph of your water.
I suppose you could use driftwood that you find, but only after you let is soak for a few days to let out any foreign substances leech out. Even then I'd be suspect, 'cause you never know about pesticides and other chemicals. Store bought drift wood is generally considered safe as it has already been 'treated' if you will. The tannins in the wood slowly leech out and I believe lower the Ph.
Then there's the peet moss method. It seems to work for many people, but to me it seems as if it's a pain to set up properly and maintain. So much work involved with peet, unless you have the time.
My tap water runs at about 7.6-7.7, and my fish seem fine. Fine enough to lay eggs and fertilize even.