Double-check all your rocks: many, like limestone, have enough calcium to keep your pH high. The usual "vinegar test" is to see whether the rock fizzes when it comes in contact with a drop of acid -- vinegar or ideally stronger. If so, it's definitely affecting your pH.
That said, don't worry too much if you can't get it super low. Don't assume every fish you see at your LFS will adapt to your water, but many fish will as long as you're on top of regular maintenance. Some of the more common commercially-available fish are domestically bred in water conditions that don't really resemble what they "should be" on paper.
So bring it as close as you can, but I'd avoid any drastic measures, especially anything you'd have keep adding and adding. If your tap water and tank conditions have a steady-state pH that's a bit high, it's easier for your fish to adapt to that once than it is for them to have the pH repeatedly go up and down.