Putting a little DE in the sand filter can help clear the pool when cleaning up the algae. Dead algae is very fine and it sometimes takes a long time for a sand filter to clean it up. A little DE in the filter should help catch the dead algae. Simply put a cup or two in the skimmer. Watch the pressure. It may rise rather quickly as it catches the small dead particles. When you backwash, the DE wiill be backwashed out of the filter. If you want, you then add a little more.