[coral reefer]

You shouldn't have a problem with Grouper! The problem arises if you introduce smaller fish or have small fish in your tank already. The small fish will end up as food for the much bigger Grouper species. Another thing to think about is the large size these grouper will attain so a large tank will be needed. With the large size comes an increase in feedings and waste, so intense filtration and skimming will be needed to keep up with water quality. Weekly water changes should also be implemented with regular a carbon regimine!
Grouper are beautiful, interesting, powerful and grow quite large, but if their requirements are met, the two will live together fine.
Oh yes, you will want to have some rock work in the tank to offer them a place to hide. This will cut down on the stress and it is also a natural habitat for them in caves etc. to hide and live happily. Just make sure the rocks are secure as their strong body will knock down your rocks possibly hurting them.