My pH had been hovering around 7.4 after I put the driftwood in, so I put some Turface in my sump and it dropped it down to 6.5ish after a few days. The pH is back up above 7, now, so I may have to change the Turface.
If you don't have access to Turface, you can pre-treat your water with peat moss. There is a writeup somewhere (hopefully I can find it) where you just put some filter floss in the bottom of a bucket that has holes drilled into it, then peat moss, then pour water over it. The water you collect will have a relatively low pH. In my opinion, that is way cheaper than using RO water, but I'm not sure about how much better it is because the pH you get out can vary to some extent; you get better control with RO.