About 3 weeks ago i bought a 3" SAL, and have been keeping him in a 32x20x18 tank with, some small tankmates, he has grown to about 4" and has gotten thicker. But i've now noticed a little nibble in the end of his tail and a little cut. He's sharing his tank with some small 1.5" Baysnook, and pbass, and feifeng. All 1.5" or smaller. I've never seen any of these pick on him. And he has plenty of hiding places, and cover. What should i do?