best algae eater for frag tank

[rfurst]

Looking for a fish to put in 20g SPS-LPS frag tank to keep macro-algae mowed down.
Any recommendations for smallish fish that will aggressively eat the algae like a tang or angel would?

 

[ThRoewer]

A good number of scarlet hermit crabs and banded trochus snails will do the job much better than any fish and not nip on corals. I got those guys keeping my display tanks clean and they are doing a great job, even with tougher filamentous algae. Best thing is, they leave the decorative red macro algae alone.
Before I had an army of 75 of each of them clean a totally GHA overtaken 40B. They got the job done in 2-3 weeks without leaving any filamentous algae. After that I had to spread them over my other tanks so that they don't starve to death.