Can you describe it the brown does it look fluffy, are the gills pale mucas looking, or red and inflamed, any flicking and rubbing against objects, any laboured breathing, is he spending alot of time at the surface of the tank.
The gills are fine. My fish is swimming around the sides a lot during the night. THe brown is not fluffy. The top of its head is turing brown. The skin is turing brown.