Dave, I added 3 about 6 months ago, and only one lasted more than a month or so. The other two never looked good from the start. At first, there was no aggression, but after a couple of weeks, the one that survived seemed to always be chasing the other, weaker ones.
Now, I don't know if the other ones were weak because they were chased, or if they were chased because they were weak. Chicken/egg.
The one that I still have is the second-favorite fish for people who see my tank (behind the flame hawkfish).