I opened my pool two weeks ago and the ph was high. Since then it's come back to normal which it usually does. The problem is my total alkalinity is high. My ph is about 7.6 and my total alkalinity is 180. The pool store says add ph down. My question is if I add ph down, that will also lower my ph. If I then raise my ph, then my total alkalinity will go back up. How do I balance this? I have a plaster pool.