Although I agree that a panther grouper would not be able to compete for food with the triggers in there, I do think that you can add another fish; IF you have a good filtration system, and protein skimmer, and are faithful about water changes! I think a wrasse would be a good addition. They are quick enough to snatch food, and stay out of the triggers way! I don't know how aggressive your clown is, but if it is like mine, you may have to be sneaky about adding another fish. Such as taking the clown out of the tank for a few days while you add the new fish, then re-introduce your clown into the 90G. Good Luck!!
