It's possible there's an infection at play too. But it's impossible to know that at this stage without some kind of lab tests, and it makes no difference really at this point. Up until three days ago, he was still swimming in ammonia. I can't stress enough just how damaging ammonia levels like that are to a fish, it's not something they bounce back from within three days, and it's even possible that the damage done was too extensive for him to recover from, I'm sorry to say. He might still be able to recover, but it's too soon to tell. Secondary infections can happen as a result of the weakened state ammonia poisoning puts them into.
Imagine someone is in hospital with third degree burns. Even once the fire has been put out, recovery takes a long time, and a great deal of care. Large daily water changes is the best medicine you can possibly provide at this point, even if there is another underlying infection, which may not be there. Please resist the urge to throw any meds at him at this point, even meds cause stress, and it's the last thing he needs right now.
It might be possible that aquarium salt could help here, I'm not sure, so going to tag @essjay and @Ch4rlie for their opinions, but I'd be cautious about it too since you know how salt in an open wound can hurt or help, depending. I wouldn't do anything other than large daily water changes for at least a fortnight though before expecting to see much difference.
Is he still eating?
