there's more info at zeobrite.com, but here's the basic skinny on it:

ZeobriteŽ
Pool Filter Media

The Ultimate Media for Sand Filters:
Provides Superior Water Clarity
Lowers Total Operating Cost
Cuts Backwashing up to 50%
Reduces Chloramines, Odor and Eye Burning
Filters Particles Down to 3 Microns
Environmentally Safe, All Natural
Replaces The Sand In Your Sand Filter
Keeps Your Pool Sparkling Clear, Naturally
Saves Water, Energy, Labor and Chemicals
Easy To Install, Works In All Sand Filters

ps- i've had to do some pretty severe vacuuming jobs lately and unlike sand, i have yet to need to do any backwashing...so i didn't before, but now i do, buy the reduced backwashing capability.