I have two gymnothorax tiles ina brackish tank. One of them I have had for over 6 months, the other I just purchased a week ago from my LFS. I thought she just had a bump on her head from the transfer, but after a week she now has a pronounced hole above her right eye, and is beginning to get one over her left eye as well. I just did a 50% water change in their 15 g tank. It is just them and a few feeder fish in with them. What should I treat this with?