First, are you sure your testing equipment is accurate? I'm not saying it isn't, but it's a good place to start. You could get a water sample tested at your LFS to confirm your results.
Second, IMO, ph is the least important test I perform. Ammonia, nitrites, and nitrates can be dangerous to fish. ph isn't really an issue until you reach the ends of the scale. The fish adapt.
That said, you need to figure out what's going on after you add the water to the tank. Put some dechlorinated tap water in two cups and add a little bit of your substrate to one of the cups, leaving the other as a control. Let them sit overnight and test. If the cup with the substrate has significantly higher ph, I'd look at changing your substrate. If there's no difference, repeat the tests with the ornaments, rocks, etc. from the tank until you find the culprit. You could also test tank objects by pouring some white vinegar on them. (Outside the tank of course.) If the vinegar foams, that object shouldn't be in the tank.
Once you eliminate the source of the ph rise, driftwood or peat will naturally lower and buffer your ph. My tap ph is about 7.4, so I added a small chunk of driftwood to my 29g, and now the ph hangs around 6.6-6.8 with weekly water changes.