Thanks alot y'all.
The Zonatus are 2 years old, they gotta be a foot long. They play nice with everybody. Now, everyday, one of the 3 will turn white and do the flaring up/staring down a fish, but no lip locking, no real fights.....so far.
There's very little fin damage, not many fights. Just the flaring. They all do it at one time or another, and as they all get older, they do it a little more often. The Zonatus do it about the same as the others in the tank.
I guess I'd say there's lots of aggression going on, but little violence. I think it's because the tank's big enough for them to turn around and go away before it gets really violent--so that's what they do.