About 6 months ago, we got our 40 gallon tank. We started off with a black moor fish and a couple of other fish – all of which are still alive. About a month ago, we got some new fish and seemingly overnight, our black moor started to develop fin rot and a white crust around both of his eyes, one of which fell out! The pet store recommended a couple of different treatments for the water including fungal and bacterial treatments, but it was too late and “Gub” passed within a couple of hours. We were so surprised as to what could have happened and thought it may be a fungus that one of our new fish brought in. None of our other fish ended up getting sick and we tested our water and it was good, so just yesterday we went and bought new fish, including one black moor. After an HOUR of him being in the tank, he looked horrible! The exact same thing was happening to him. His fins were destroyed and one of his eyes was already starting to pop out of the socket. We immediately removed him from the tank and took him back to the store to that they could hopefully offer us an explanation, but they were just as surprised as we were. All of our other fish are perfectly fine with no signs of fin rot or disease. We do have a cichlid that they say may have been aggressive toward him but I can’t imagine he could do that much damage within an hour?! Any thoughts!?