Grouper in a Reef Tank

Has anybody here ever kept a grouper in a reef tank? I don't even know what kind it is. It says it's a spotted grouper but it doesn't look like a spotted grouper. It's only about two inches long right now and they want $20 for it. It is white with very bright blue dots. My inverts are a sally lightfoot crab, hermits, snails, and a brittle star. I'm not sure if they would be at risk. I also have a pretty big maroon clownfish in the tank. I have really wanted a grouper but am reluctant to get something that could potentially clean out my tank. Any thoughts. Maybe I could trade the crab in for credit.