I bought a tank a few months ago and fish cycled the tank using danios and tetras. I now know that's not cool, but I was working on limited advise. After a few weeks the largest zebra danio started constantly chasing the other fish in the aquarium around. The tetras would hide behind a large rock and he would seek them and the other danios out. I read that they might need more than 6 fish to give a more "school" like atmosphere so I added some mollies (3). The behavior stopped and I thought I had solved the problem. About 2 days ago the behavoir started again and he won't stop with the aggression. He chases any fish that's near him and seems to nip them if he catches them. I am about fed up with the behavior. The girl at the pet store just suggested removing him, but I want to know if another method exists to stop it. I thought danios were supposed to be nice community fish.