a clean up crew is never a bad idea. i dont know what you are wanting, but the best and what most use is usually a mixture of snails and some small hermits. the bigger the hermits the more they seem to prey on the snails for their shells. snails help on keepin the glass clean, and the hermits will help with the grooming of the substrate. are you going to incorporate an anenome at all for the clowns to host?