I have used the magnum canistar 300(350) filter as both a diatom and carbon filter media. Diatom filters are considered water polishers. They take out almost every large particle! However, they are both messy, and a pain in the tail to run. I ran mine with diatoms twice the whole 7 years I have had it, otherwise I kept charcoal in it. Why did I run it with diatoms? Dunno, just had the ability to do it, so I did.