I have a 29 gallon tank with the following mates: 3 dwarf gourami's (1 male, 2 female), 8 neon tetras, 4 rasbora's, 1 clown pleco, 2 clown loaches, 2 black phantom tetras and 2 albino cory's. Total of 22 fish. I work beside my tank at home and never witness any fin nipping or real aggression. My poor little albino cory's have been without their fins for months now. I had a group of serpae tetras about 8 to 9 months ago and they were such bad fin nippers that I took them back to the pet store. It was at that time the cory's came up with nipped fins, but ever since then, they haven't grown back and have actually got worse, so I'm thinking some other fish is responsible. Could it be the clown loaches and are they doing it at night while I'm not watching? I can't figure out why only the cory's are effected. Anybody have any thoughts?