There are not many things that will eat algae off of a coral. Corals sting...
Good snails
Mexican Turbos, astreas,, nerites... I prefer them in that order as far as being rock/glass grazers. The ceriths will burrow in sand too.
Ceriths will burrow and keep a shallow sand bed clean.
Tuxedo urchins are good too.
Black Fuzzy Chitons, some stomatella snails.