Pat, Thanks for the help. I have a vinyl pool. I have not noticed bleaching of the liner at the high chlorine level. I have not vacuumed to waste. I backwash to waste. My pool drains very quickly if I vaccuum to waste, and I live in Kansas and am under severe water restrictions. Today at noon my pool was at 20 FC. Five hours later it dropped to 15 FC. How quick a drop in FC is acceptable. I was in full sun today, and I see no algae now. Also, during the day, can I leave my solar cover on to preserve chemicals and shield them from the sun? Dorie