There is a trick of adding a little DE to a sand filter to get better filtration if you're looking to trap really small stuff.
Check this thread:
http://www.poolforum.com/pf2/showthr...to-sand-filter
The first post tells you the process. If you do this just keep a close eye on the pressure as it will rise quickly if you're catching stuff.
You then backwash and start again. If you really have a mess, like I have at times, I just do a quick backwash to dump most of the crud. I don't try to get the BW water totally clear until I've eliminated most of the crud. Saves water.
Al