I don't know what to do 
. I have a small 15G tank that has 3 little clowns in it.....because it is a fairly new tank I am still trying to deal with algae. I added a 3-4 hermit crabs and several snails to help get raid of it, but the hermit crabs kept killing the snails (even though they already had a bunch of empty shells)......I went to my LFS for suggestions, and they sold me 2-3 large turbo snails and said they would be safe because they were bigger than the crabs.......... the crabs got to 1 of them but the others made..... on another trip, they suggested I add a sea urchin to my crew...... I did, but now the urchin killed the snails by wearing them as hats and/or the snails are not "cleaning", if they spend their time in a tour of the tank on top of the urchin 
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. any suggestions on what I can add to my crew???