I've heard of using distiled vinigar to lower ph as well. The only thing I've actually used is different forms of blackwater extract (humic acid, and tannins). The problem with that is that you have to use a TON of it in order to eat up the buffering capacity of your water before the ph will drop. By that time I got to the ph I was shooting for (6.5) my water was not just tea colored, but more like weak coffee colored. I could barely see my fish.
