Adjusting life sand volume to make up for lack of liverock
 

im setting up a 33gallon tank for 2 clowns and an anemone, and a few inverts (cleaner crew), im only planning of putting about 20lbs of liverock and im wondering how much live sand i should be using

General rule is a a pound per gallon or so i think, I like keeping the sand beds thinner personally they trap a lot of crap and can trap deadly gas pockets if stirred can wipe out your system. I usually run with under a 1/2 inch or so and it has never caused me any problems.

Based on what I've read, this sounds like a lightly stocked tank so you should be fine. If you find you are having problems the next step would probably be a protein skimmer.

If you want to go the less conventional route I've been looking into deep sand beds (DSB). These are typically 4 - 8 inches deep either in your display tank or in a sump. Ron Shimek is a proponent of DSB in your display tank. He has a forum on at marine depot. The other person I've read about is Anthony Calfo, a commerical coral farmer. He advocates aggressive skimming plus remote DSB (in sump). Check out DSB in a bucket for nitrate control at ReefCentral.