One of the neat tricks we've learned is that if you add a little bit of DE to your sand filter, it filters much finer stuff. I use less than 1 cup of DE. You add just enough to raise your pressure about 1 lb. It can be anywhere from 1/4 to a full cup. You add more after you backwash. DE is amazingly cheap when used this way. I'm not even halfway through a 10# box I bought last summer for $8. I MAY finish it this season, but the results are incredibly good.