I came home the other day and went to feed my Koi fish when I noticed something had bitten one of my koi's back. There is a really good size chunk out of its back and you can see the koi's spine. Amazingly enough he is still alive and this happened 5 days ago. What can I do to help heal it's back? I moved him from the outside pond to an aquarium inside the house to try to keep it from getting infected.