ive just found this on the illness page its the same thing my fish have but mine have got some holes deep so if its an ulcer like the person was told have i been treating the wrong meds and thats why its not heling heres a link its the orange fish at the bottom
https://www.gardenpondforum.com/photos-my-fish-need-help-t5461.html
https://www.gardenpondforum.com/photos-my-fish-need-help-t5461.html