I'm a newbie here, I don't have a complete test kit yet. I cannot keep chlorine in my in my pool. I have an In ground 15000 gallon pool. The pump is a pentair 3/4 horse pump circulating 24/7. My filter is a DE type. My chlorinator is a king with a zinc/silver cartridge and a frog chlorine vac pac. I shock once weekly with 1.5 gallons of 12.5 liquid chlorine. My pool temp is maintained at 87 degrees with a heat pump. I live in Ohio, my pool is heavily used and I have an auto cover that is closed when the pool is not in use. I shocked last on Sunday, I OTO tested Monday and chlorine was normal. 4 people were in the pool today(Tuesday) I retested today after swimming and I'm back to 0 ppm chlorine. CYA was last tested at 86 ppm. I've used 8 going on 9 cases of 12.5 chlorine from Memorial Day to date. Why can't I balance this new pool?