ph was low, that is an indication something might be amiss in your tank. Do you do regular water changes? Do you have aragonite as a substrate--both of these can be solutions to a low ph, as can protein skimming and good water flow (increased oxygenation). In answer to your quesiton about water flow, BTA's appreciate randon, moderate current. I wouldn't direct a power head right on it, but it is preferable to have some type of wave maker, or, at the very least, two power heads that will give some random water movement. As I'm sure you have heard before, make sure the intakes to the powerheads have sponge covering them.