A sand dollar?! Can you post a picture of it? Where did you get it? What does it eat?

For clean up crew, I have a tank of similar size to you 30G, I have 2 nassarius snails, 5 astrea snails, 1 mexican turbo snail, 1 regular turbo snail, 1 pink emerald crab, about 8 small hermit crabs. Everything stays pretty clean. I have even a bit too many I think, I feed them nori sheets sometimes if things are looking especially clean. I am actually going to move the mexican turbo snail to my 90G, put him to work.

Be careful with hermit crabs. I have the blue legged variety and I caught one taking bites out of a snail... Then the mighty hand came down apon them! :lol: