Not to sound like a smart aleck, but it depends on why it is low. Excess CO2 in the room can drop it, as can some supplements. Kalkwasser raises it, as do pH buffers, and an environment with less CO2/more oxygen. Some "tight" houses have a lot of CO2 in the air, and running the air line to your skimmer from the outside of the home can help that.
I'm not a big fan of dumping chemicals to chase pH; if your parameters are in check then acceptable pH should follow.