One website recommends the following:
10 Scarlet Reef Hermits
20 Turbo / Margarita Snails
30 Red Leg / Left-Handed Hermits
or
1 Abalone
2 Mithrax(Emerald)Crabs
2 Impatiens Cucumbers
1 Black Hawaiian Brittle Star
1 Red or Black Banded Serpent Star
1 Red Fromia/Orange Knobby Star
10 Burrowing Cerith Snails
I don't know if I conquer with the Orange Knobby or the Cucumber, but a mix of hermits and snails are standard. A brittle star will help keep the deep substrate clean. The emerald will help with any type of valonia (bubble) algae. The abalone will do a great job keeping your glass clean. HTH,