A snowflake,a huma, a panther grouper.Now what?

[predator]

I'v got a 75 reef as well as a 75 predator and I'm up-grading both.The reef to a 3ft by 3ft by 18in and the predator to a 150.I'v already got a snowflake who's about 18in, a huma trigger who's still pretty small, about 5in and a panther grouper who's about 4in.I want to add another fish to the tank and I'm curious as to what you think.
I know I'm going to have to get rid of the grouper or do another up-grade.Any suggestions as to what could take his place as well.My brother has a 240 that is still under construction.He wants it to be a predator and said he'd buy the grouper for good money in the next year or so.

 

[tomato clown]

What about a Mexican Parrotfish?
One of my LFS had a setup with one and he was just as big as a grouper.
I dont know much about your fish, just mentioning what I seen being you asked.
Dan