I have a 4 year old featherfin catfish (3-4 inches) that has lived with some angels and ghost fish for the same amount of time, 4 days ago they were all moved to a larger tank. This tank has been running for about 2 years but was recently emptied and water changes done over 2 days, it was then left to stand for a week with 2 pumps running. The catfish seemed to love it and spent 2 days patrolling the tank, problem is the dorsal fin on the catfish has become swollen and rotted and along it's back there is a white growth which doesn't look like any fungus infections i've read about. Apart from that his behaviour seems normal and none of his other fins are affected, and no other fish in the tank have become sick.He was thrashing quite violently when we moved him, is it possible that he damaged himself and this is an opportunistic bacterial infection, how would i treat this? I'm a bit wary as the last time we put a bacterial treatment in the water last year every fish was paralysed and it took rapid water cycling to recover them (lucky we didn't lose any!)
