That stinks - unfortunately I can relate - you just need a bigger tankThey don't all get on. They don't kill each other, which I think is about all I can expect. There's usually a fish in there that's a problem.
Last few months, it's been the Zonatus. I have a BEAUTIFUL Melanurus male, 12 inches or more, living alone in my sump because the Zonatus decided he just had to go.