That's a nice big filter which is good. Your pool store should definitely have DE. DE is the media used in DE pool filters which are common so I can't imagine that they wouldn't have it.

Let us know how the DE test goes.

(By the way just for future reference, sand doesn't really wear out or need replaced. Many of us have the same sand for years and years and years. It occasionally needs topped off but doesn't actually need replaced. (Unless you convert from Baquacil to chlorine or something like that because Baquagoop really gums up the sand.)

EDIT --- Why don't you update your signature and add your filter capacity of 350 lbs.. You can click on the link in my signature to do so.)