The peice of driftwood in my 29 gallon tank dropped the ph to 6.0!!! I'm going to do a water change, but I want to know how much crushed coral I should use so this doesnt happen again, keeping the ph at 7.0. the driftwood is approx. 10 Inches long, 4-5 inches wide, and 2-3 inches deep, and shaped sort of like an oval.... Please Help!!!!! I never had this problem in this tank before the driftwood, but I need it for my royal pleco!