My Fish has an unkown disease! It has claimed 2 victims already! Can someone please help me? FISH ARE DYING!?

Help! Ive posted about this before on another question page and no one could help me. About 6 months ago, a male molly of mine got an odd spot on his belly. It looked much like a fungus so i promptly treated the tank. Symptoms didn't improve. The spot continued to get larger over the next view days. It was located under the pectoral fin and to the right on his right side. The spot didn't get much larger, but the strange part wasit began to get deeper. It began to eat away through the scales, the skin, and later i could even see his bones. I had had him seperated by now so i knew that no fish was picking at a fight wound. I was about to euthanize him when no one could help me but when i got home from school, his organs had com out of the hole. It is believed that this disease took my Ghost Knife Fish about a month ago and now a male swordtail has it. I do not recall on the Ghost Knife Fish but i think it was always on the right side. Please someone help me! Ive tryed everything!! =(