On sunday my ph was 8.0 and my hardness was 140ppm. the pool store computer told me to add 4 lbs of ph down and 25 lbs of hardness control. I added the ph down on sunday night and only 7 lbs of the harness control on monday and another 7 lbs yesterday. Today my ph was 7.2. is there a correlation? What actually is the "hardness control?"