Have you owned a scat? A red one at that? there the most aggresive ones around, they attack and keep attacking. Mine killed 3 silver scats 3 days after the red scat was introduced. Discus stand no chance mate.
I second Camo X's opinion, Scats are mean. Can be kept in freshwater, but better with hard water and tons of aquarium salt. Given those conditions, and their temperament, there's a reason you usually only see big ones in African cichlid tanks.