cerith snails and trochus snails are the best cleaners ever, IME. trochus eat like pigs, and have the ability of righting themselves if they fall over (instead of drowning) and cerith just do an all around great job, spending time int he sandbed, on the rocks and on the glass, plus they spawn readily in a captive environment! good stuff! scarlet hermits are also good grazers, as are blue leg hermit, but blue legs tend to be a littel meaner and might eat some of you snails. if you have problems with bubble algae, you moght try an emerald crab, sometimes they eat the stuff, sometimes they dont, and maybe some peppermint shrimp as a prophylacctic, in case any aiptasia anemones decide to pop up. this is what i have in my 20 anyway, oh and maybe a florida fighting conch to help the creiths move the sand.
hope this helps, and good luck
jon