well, i know of a few people who have used longspine urchins, but that might result in the injury, or death of the trigger, so becarefull. water changes might be the best bet, combined with low ligthing.
I get one of those "125g cleaner crew" packs off liveaquaria about once every year and a half. . . it keeps the supply going. I believe it gives my picasso a bit of variety in its diet.