For the CUC you thinking of crabs and snails or just snails? I like Florida Cerith, nassarius and astera snail, I like how the turbo snails clean up algae but they are bulldozers. Crabs emerald and a couple of hermit crabs if you are going to have crabs in the tank. Some people like crabs and others don't one of my tanks doesn't have any in it but that is just because I have a coral banded shrimp that would probably kill them.