Welcome to Simply Discus! Sorry for your problems. Can you post a photo of this discus?
First off, I would lower the temp to 81-82. Higher temps promote bacteria. General Trio powder has some good meds in it and is a good med, but it's also why I prefer using targeted meds. If this is an internal infection, as I suspect, nitrofurizone is for external issues. Kanamycin alone is recommended for internal.