Yes, that's what I suggest too, get your total up to 5 and harmony should return! I have had a couple of aggressive discus in the past and some of them are aggressive no matter what. One of the worst ones I had was a red marlboro, no matter what I did....rearrange, took her out of the tank and used her as my "sacrificial lamb" in the QT tank with new discus to ensure there were no issues....she didn't care. She bullied everyone, new discus, old discus, even in a large group. I rehomed her to a friend I used to work with.