I believe he is fighting both Hexmetia and a bacterial infection from the tailrot. You can use another antibiotic along side the MetroPlex so to address the tailrot infection.
If he were my fish, to fight the external infection, I would dose the water with SeaChem KanaPlex antibiotic and add a little to his food as well. SeaChem recommends using SeaChem Focus to mix KanaPlex into food and sprinkle a little SeaChem GarlicGuard to stimulate his appetite.
FYI, in the last two days I had to dose my Discus with KanaPlex to fight a tailrot issue. With one dose and in two days, his back dorsal and anal fins getting color back, and the shredded lower anal fin healed together, with color coming back. KanaPlex works well. He was getting tailrot from not eating well and having to fight for food with Roseline Barbs. I been trying to get him to eat flake food instead of only bloodworms but he is winning the fight.