I had a panther grouper in a 75 for 4 years before I donated him to a Local seafood restaurant display tank in Mobile Al. He hadn't so much out grown the 75 as it was the size of food source had increased to where it included a lot of the fish I wanted to keep. It was in my beginning years of saltwater. I had him in with a Snowflake moray eel, after a month went by they developed a pecking order for feeding time when feeding them live shrimp. It took a u shape chunk out of the left pectoral fin on the grouper to get it across to the grouper to let the eel eat first then suck up the majority of live seed shrimp that was left. As for the fins they look like they need to be treated for fin rot.