not sure on how to treat but i do know that its bacterial and most certainly connected to bad tank maintenance, you should be able to find the treatment on the web somewhere but i would suspect melafix and decent water changes will do a world of good.
its easy to say what the treatment is and i believe this is where many forums go wrong, they rarely identify the reason why this has happened only the cure. can i ask how much water you change each time and how often you do change it?