I will give that a try if I can find DE locally. I've about decided to change the filter sand (starting the fourth year on this). It probably is needed so it won't hurt. At least I'll be able to dismiss that as a possibility. The pool seems to be clearing although at a very very slow rate. It could have residual algaecide or suntan lotion, etc from last year. I ordered the TF100 test kit today so I can get better numbers on high chlorine levels. I will continue to shock and filter. Thanks for the encouragement.