Hey, I am wondering if any one can help me, I am sitting with a butterfly koi (not a show fish at all) which develope a lump just below its fin, it appears to be something sitting on the skin or under the skin and is more or less the size of a R5 coin. My first impression was that it is an ulcer so I took the fish out of the pond and put it in the quartantine tank and treated it with three baytril injections two days between each one. Nothing has happended and it still appears to be the same. It is there for almost a month now. As I said it is not a valuable fish but I would like to know what it is because it can happen to my show fish aswell and then I must know what to do.