Perfect pH eliminates pH drift which lasts from refill to refill. Easy to use and convenient liquid raises and/or lowers pH for simplified water chemistry. pH control is important and should be checked regularly for proper water balance. Local water conditions or heavy usage could cause pH to rise or fall. The unique buffering action in Perfect pH will allow the pH to lock in the proper range and minimize the need for additional pH adjustment. Lasts from one spa refill to the next. Test spa water pH levels with 4 Way Test Strips.