About thursday my foxface looked like he had some sort of bacteria that was on his fin. I didn't know what it was and i had no time to go to the store and get some medication, so i hoped that he would be able to survive by this weekend. Unfortunately, he didn't. I examined him before i flushed and saw that most of his back fin had been rottened away. Can someone explain what my fish had so this problem will not occur again?