Can anyone identify this disease?

[Xarga]

Hi, I’m two months into my first Koi pond and have gone through the challenging phases of new pond syndrome And finally happy with the chemistry and stability of the water. Someone very kindly donated five large koi Between 14 and 20 inches long. Sadly, one of a Koi came with a large ulcer At the back of the head which the previous previous owner said had been much the same for the last 12 years and had not infected the other fish in his overstocked koi pond. The behavior of this fish Is to cruise around the pool very slowly. He’s lethargic compared to the others, but his appetite seems unaffected. His coordination when targeting food on the surface is poor and his vertical balance isn’t always good. I think he’s about 20 yrs old and is about 21” in length. It seems to me that the ulcer is getting a little bit worse and I would appreciate any advice on whether this can or should be treated in any way. I would love to be able to improve his situation

Water temp 45-49
Ammonia 0
Nitrites 0.25 ppm (peaked around 8 during NPS)
Nitrates 10
Ph 7.2
Wide range PH 8
Total alkalinity 70
Carbonates 80
General hardness around 400

 

[j.w]

@Xarga
I'm not good at figuring out diseases so I'll pass this onto someone else. Hope it is nothing that the poor fish can't live with tho.

 

[WaterGardener]

The folks at Koiphen.com may be the best people to help you. They are very familiar with koi diseases and ulcers and their treatments.

Best of luck with your fish.

 

[Tula]

I agree with @WaterGardener , koiphen.com will be your best source of health information on koi. Hazarding a guess, the location of this ulcer leads me to suspect a heron strike. The strike obviously didn't kill the fish, but led to a serious secondary infection.

Please post again and let us know how the fish is doing.