Clown triggers are notoriously delicate as small juveniles, nice, if a bit rough as medium sized fish and finally, usually turn out to be homicidal maniacs when they reach adulthood, assuming that you've gotten to the point where your fish live years, rather than months.
Many of the larger Triggerfish become extremely hostile and vicious as adults, and when you combine the tough, leathery body armor with very strong jaws and teeth that would make a boltcutter look dull, thre's not much that can stand up to them.
A 125 would house one adult Clown trigger, based on space (imagine a football in the tank and you're close) and as far as personality...well, an adult Clown, Queen or Titan trigger will show you exactly what I mean.
The worst of the smaller triggers is the Undulaus, which only grows to about 11" but will almost always kill everything in the tank at 1/2 to 3/4 that size.
If this sounds like I don't like triggerfish, it's not true....they are active (spelled: need lots of room), highly intellignet, have great personalities and beautiful, but many will need a tank all to themselves, much like a Lion or a Tiger.
It's just the nature of the beast.
Mike