I have a 16 foot above ground Intex pool. It was covered for the winter and not treated. I began treating three days ago and my water is still green. It is a lot lighter green, but still green. I have been maintaining a chlorine level of 15, back washing my sand filter multiple times a day, my CYA is 30 and my PH is 7.2. What am I doing wrong? I thought my pool would be gray by now.