So one of my bloodfin tetras as a serious problem, mainly in the area of the back fin. I first noticed that his tail was badly damaged a couple days ago and I figured my golden gourami was the culprit. I separated him from the gourami but the tail only seems to be getting worse. In fact the back fin is almost completely gone! I've since moved him to an isolated sick tank where the Melafix can really sink in. Can anyone tell me if this is tail rot or simply a natural reaction to a badly nipped tail?
The first image is before I transferred to iso tank. The lower image is after transferal, a day or so after the first one was taken.