I have a 45 gallon with about 60lb ls, 30lb lr, 5 damsels, 12" carrot sponge, 2 - 1/2 inch peppermint shrimp that hijacked on a lr. I need a "clean up crew that won't eat my shrimp since i am planning on keeping them. Thing is... What is a clean up crew and what will they do for my tank? I read...