Why dont you try to keep them both together? I have a miniatus with a spotted grouper. They leave each other alone unless the spotted grouper tries to hide in the miniatus's hole, then he gets chased out. The miniatus does this to all the fish in the tank though, then he hangs out with his head sticking out and opens his mouth a bunch really wide to let them know whose boss, very funny to watch. Now they leave his hole alone and he doest bother anyone. My spotted is full grown and is large enough to eat half the fish in my tank(including the miniatus), but he is well fed every day and is super chill. You should be fine with those 2 fish, panthers get big but are wimps compared to other groupers like a miniatus. Try it out if it doesnt work I will take your panther for sure.