I have a 29 gallon tank with 5 Diamond Tetras, 3 cories & one small angelfish. I haven't seen any aggression but noticed today my angelfish seems to be hiding. I tested my tank with the API kit & Ammonia is 0, Nitrite 0 & Nitrate is 5.0. Could the Diamond Tetras be bullying the angel. They have been together in the same tank since March.