Hi bert, I just read your posts, I am very sorry to read about your problems, but I know how you feel.
We experienced this problem in our pond last year. We took all our fish out into a holding pond while we were making the main pond bigger. Because the holding pond was shallower it encouraged them to spawn. Several damaged themselves and one got damaged the injury turned into an ulcer. Eventually we got the main pond running and returned the koi back into it. But the ulcers did not go away they just got worse. We treated with machalite and formalin plus various other stuff but it did not help. In the end our koi dealer gave us a number of a vet , the late Louise Andrews, and she gave us a visit. She took out one of our koi with a mouth ulcer, put it to sleep and did a altopsy. She confirmed that it was aeronomas (bad bacteria) etc and we needed baytril (anti biotics) and told us to change atleast 20 percent of the water every day! (this would keepthe bad bacterial down) She told us to seal all the wounds on the koi. For extra support and advice we join Essex Koi club, they were very helpful and supportive. The fish had two courses of antibiotics and eventually we got rid of the ulcers. I've got a pic of the one which was put to sleep. The others have healed up ok. But looking back it was a combination of several factors:
They spawned in the holding thank which made the water quality poor, amonia should be zero, nitrite zero if not the fish get stressed and their emmune system fails and thats when the nasty bugs get in.
If a fish has lost a scale treat asap by cleaning the wound and sealing it this stops any bugs getting in (any koi dealer will have this). If it looks infected get the fish out and quarantine it, it will be cheaper to treat it and will stop the infection spreading to other fish in the pond.
Hope things get better soon
