I have a 24 ft round pool 4 feet deep grading to about 5 in middle, vinyl liner. I am told that i have 15000 gallons of water. The test I listed was done by pool store. I have about 5 gallons of liquid chlorine on hand. I added 1 gallon of liquid chlorine last night. Reading is about 3. This AM my husband dumped 10 pounds of calcium up in the pool. We will not use the other 40 pounds they sold us. We will begin to dump pool this evening. Should we empty 1/2? When can grandkids swim?? How long would I keep the chlorine at 15?