I have a 16500 gal above ground pool. I use a cartridge filter with 1.5 hp. I replaced about a quarter to one third of the water volume when I opened up the pool. I tested the water and took a sample to my local pool store expert. PH, Alkalinity, CYA all within acceptable limits. I put in about 3 lbs of shock (Calcium hypochlorite) followed much later the same day by about 2.5 lbs of chlorine (sodium-dichloro-s-triazinetrione dihydra). After a day the pool registered free chlorine at about 3 ppm. I put in another 6 ounces of chlorine as maintenance. It was raining. Today less than 24 hours later, it is sunny and there is no trace of Free Chlorine. I have never gone through chlorine this fast. Please help me understand what is going on and how I can fix it. Thanks.
Thanks for you reply. I will be purchasing a better test kit and getting back to the community with better results. I just returned from Leslies. The tech there told me told me that the FC = 0, he did not provide a number for CC. PH = 7.4, TA = 100, CYA he did measure directly but in a previous test a few days ago I was told it was 30, CH was not measured. Strangely he used an Aquacheck strip to check the chemicals instead of the usually liquid agents. I had an algae bloom today in several spot around the bottom of the pool wall. I am in the process of treating same with shock.