I think the answer you're likely to hear is, I don't know or it depends. Damsels in general are aggressive for their size. I have a Talbot, two yellowtail damsels and a clown in my tank (Reefer525XL) with a slew of other larger and more aggressive fish such as wrasses, tangs, and a trigger. I have found that my damsels picked a 10" x 10" spot on the reef and tend to stay there. Fortunately the yellowtails and Talbot picked opposite sides of the tank. Occasionally, they will get too close and when that happens they fight.
Few other things that tend to affect compatibility:
- Size of the tank. You have a 4 footer so there's room for them to remain naturally separated.
- Size of the Damsel. In my experience a larger one will pick on a smaller one. Equal size is probably best.
- Number of other fish. Again in my experience with multiple damsels or even tangs, the more you can disperse their aggression and attention the better. Having other "targets" swimming by tends to provide distraction and limits aggression.
- Size of other fish. The damsels leave larger fish alone. They also generally ignore the sand dwellers.
- Feeding. If they're fed enough there might not be the urge to fight for food.
I also have a Domino in my sump. He was in a second tank of mine with a larger clownfish. They two would fight non stop. He's still in the sump because I know once he goes into the display the odds are slim that I would be able to get him out if I had to. I would urge you to sleep on it a few nights. How attached are you to the other fish? Can you accommodate multiple small feedings per day? What is your ultimate stocking plan? Can you pull rockwork out if you need to remove the fish? In general I dislike adding fish because it disrupts the equilibrium that's been established, as a result I tend to give it a real good thinking before making additions.
