I have a new gunite salt water pool that was installed last year and plastered the first week in May of 2012. From May until the time I had the pool closed in late Sept. I battled the PH levels constantly rising because of the plaster curing, which I was told was normal. However, when the pool was opened in May of this year I had a scale problem that was so bad the pool had to be drained and hydro-sanded. The pool installer argued that the plaster was fine and that there must have been a chemical imbalance in the water over the winter. Since I did my own water testing and also had my water tested every other week by 2 different pool stores throughout the season I threw in the towel this year and hired a pool professional to do my maintenance. However, the same problem has been going on again this season. Since June the pool professional has been adding 1 gallon of muriatic acid every other week and for the weeks he is not adding muriatic acid he is adding 4lbs. of PH down. The pool is 18,700 gallons and I have a salt system. My question is whether this is normal and if not what's driving the PH to continue to rise? My concern is also that I will have the same scale problem next season when the pool is opened again. Thanks.