I went to my LFS with only the intentions of buying some new media for my filters. I decided to check out what new fish they have and come across this 20 inch hybrid stuffed in a no bigger than a 40 gallon tank. As I watch it trying to swim around I notice one of its gills curled. After a few minutes I decided to buy it and try to heal its gill curl. Where do I start? I have done a big water change, added salt and Melafix.