Hi "Cabbage",
I realise that you posted this mail over a month ago but I just came across this forum today.
You mention about a growth on your fish. I am not a fish expert but I think of three causes:
1) non-malignant growth
2) bacterial infection
3) cancerous growth
Do you have a vet nearby that treats fish? I recommend that you have your fish examined by a professional.
I am fortunate to have a vet not too far from where I live, who treats fish, because it seems that many small animal vets in the UK do not treat fish.
My fish had a little white spot on his lower jaw. Over time it developed into a pinhead. Then it began to expand and start to look like a cauliflower shape. I could see tiny bloodvessels wrapped around the tumour, feeding it. The development from a spot to a lumpy growth took a long time, I think a couple of years. Finally I thought that the lump might start to bother my fish when he is eating, so I called the vet that I mentioned above. The vet anaesthesized the fish and cut away the growth. This was over a year ago. The vet assured me that the growth was non-malignant but he also warned me that it might come back. Thankfully, so far it hasn't.
Just to let you know there may be a treatment out there for your fish; I think your first call is to find a qualified vet.
Best wishes
Regena