Had to deal with the same thing right now with my brother in law, and already had to take one flower horn out. It was only 2 inches, and the aro is about five, and the FH was taking small pieces out of it's fin. FH are generally not too picky about water parimeters as long as it's stable, around high 70-low 80s. My own rule is to keep water at low 80s to keep ich at bay. Hope info helps.