I got a close up of the wound
It's a bit blurry but you can kinda see how deep it is. It also kind of smells around his tank. (That could just be normal fish smell though)
It's an open wound, and it looks like he's missing some scales. I'm not sure if it's an infection or if one of the snails in his tank decide he was tasty.
He's not lethargic, and still eats. We're going to get him some antibiotics (I don't know which ones to get) and some aquarium salt. We...