Even though your decor is dull, it could still be an abrasion if the ornate was trkying to squeeze in between a spot, especially after eating a meal and it had a bulge in it's belly.
But usually, I connect red irritated areas with bacterial infections. Melafix, or Maracyn are what I would use.
Plus big water changes. You have a lot of algae in your tank... what are you WC's like?