I have a 20 gallon tank with 30 pounds live rock, 15 pounds live sand. 2 clown fish. I need to know how big of a clean-up crew I will need to keep this tank under control. I currently have 3 snails and 2 electric blue hermit crabs. It has been a week and they haven't even put a dent in the algea. How many more snails, hermits, or shrimp should I have in my 20 gallon tank? I want variety in my clean-up crew so if you could tell me good combinations of species that would be helpful. I am also interested in getting some kind of crab.