Thats pretty bad man. You need to treat with meds asap or the bacteria/fungus will continue to eat away at the wound. Any LFS/Petco or anything like that will carry Melafix. A natural oil which destroys bacteria and fungus while promoting healing. I would also add a teaspoon of salt for every 10gal of water. This will help with stress.
Pimafix is made to work in conjunction with Melafix which sopposably is extremely effective, But Ive seen great results with just Melafix and salt.