I have 4 clowns in my 75g tank... Got them all from someone else who had them in tank... after about a month in my tank, 1 started chasing 1 around like mentioned above. wouldn't leave this poor clown alone.... other 2 clowns were fine and didn't join in...
anyways, I put the small one being chased inside a tall glass container and put a net on top... i put this right in the tank as i didn't have much LR yet... left that little guy in there for a day and the bully realized it can't get it anymore. i let it out next day to take a risk and see what happened... and from that day on all 4 our friends again and no chasing at all. month later and they are fine and now i have tons of LR so they have plenty of space.
that's my story, and I'm sticking with it