I am no pro here, but because it's a blue colour like the rest of the fish
it could be a simple ulcer, I can't make out if the skin is broken, if the
skin is broken, then it might be a parasite, there should be some medicine
for that. If it's just a lump/ulcer then I imagine there isn't much you can
do. I had a skin damaged fish here for a while and had it in a separate
tank, after 4 weeks it was as good as new.

If you see something similar on other fish then there night be something in
the tank that is doing it.

Have you got a UV light on your system ?
Have you got any stinging creatures in your tank ? (Like an Anemone)

Can you post your water parameters too, someone else here might be able to
give better advice when they have more information about your tank.


Thanks for the heads up! I did post a pic there

If anyone has time to look at a picture let me know. I will email it to
you. Simply reply to this with your email address and I will send
photo.
Remove "nospam" from my address before sending.