I have a ten gallon tank that housed a veiltail betta and 4 cory cats. One morning I notice a dead cory and my betta's tail is destroyed. The dead cory was also missing parts of his tail. I concluded that this was tail rot and ran to my LFS to get meds. By the time I got back my betta was dead. Fast forward to the next day and I have a cory that was missing parts of his tail and actively dying. By now I've started the Tetra all in one treatment. Now on day two of treatment I lost another cory. He tail was intact but he had to have just died when I noticed because he wasn't floating yet. I've had trouble keeping ammonia down because of the dying fish but other wise everything is where it should be. What else could I be missing?