Snails are some of the best clean-up critters you can get, better than hermits. Nassarius, ceirth, and a good mix of a few other snails will keep everything clean.
For your tank a pair of Fighting Conch, a dozen Nasarrius, a dozen Cerith, a pair of Black Atlantic Cucumbers.
And, some high quality live sand that contains worms & other sand bed infauna.
Urchins aren't usually reef safe, from what I understand. I don't have personal experience with them.
My conch is making me mad! He was hard at work for weeks and then got fat and lazy and has buried himself under the sand. Get out and work!!