My 2 cents. I’ve got the exact same fish with the exact same problem. Once he was moved into a hospital tank, he coloured up and lost stress lines within a few hours. Just added a bit of rock salt and kept temps at 28 C. He is not out of the woods yet but looking much better . Although has gone off food since being in hospital tank. Holding off meds for now, just clean water and salt. Also just to clarify, I am in no way an expert or experienced keeper but just sharing my current experience with this.