Ok.. Sounds like right now you need to treat him for bacterial issue. Id recommend a gram negative charged bacterial treatment such as Kanamycin Sulfate. Seachems Kanplex is a good choice for that. It does a great job as it is an easily Skin absorbed antibiotic. It does great with open red sores or ulcerations along with other things. Kanplex can be combined with other medications such as Metronidazole. Thus id also recommend some medicated soaked food such as with Metronidazole. You could even dose some Metronidazole in the tank safely.
Id do the recommended dose for the Kanplex along with associated water changes and the Metro soaked food.
Id do the recommended dose for the Kanplex along with associated water changes and the Metro soaked food.