I have a 2 year old dragon scaled male betta (Iroh). He is in a 5 gallon heated and filtered tank. 5 days ago I put a platy in with him, who is currently doing wonderful. Today Iroh was hanging at the bottom the tank more than usual and I noticed dark to black discoloration on his side and posterior back. He can swim, although he's very lethargic. I put a pH neutralizing tab just in case that's affecting his energy, and I put a safeguard tab in as well. Anyone have any idea what he has?