Yes, I have heard of it but never seen it. I read that it is "mildly contagious", a viral illness that as you said is harmless. How has your fish been acting? Lisa

Lisa,
At first I took the fish out and put it in a separate tank, where it hid. But after reading that it wasn't contagious, I put it back in the big pond. He's swimming around and eating with the other fish...I did notice that he is the smallest koi that I have...perhaps the weakest. Our weather hasn't been consistently warm, so he still has a few blotches...

Koi Pox will come back ever year to same fish once it had it when ever it gets cold. It is very rare that it ever hurts the fish. Normally it will go away once the fish warms up.
Mike