With the ice receding some more, I saw and removed 2 dead 7" koi today. I'm not totally surprised, but certainly disappointed.
One koi looked like it had died quite a while ago, the body was almost a half empty shell covered in white fungus and the other was still a plump body, but still quite covered in white fungus.
Both were floating just under the ice.
The last time I saw all the fish was middle of last October I think, when the water was cooling down and they were staying near the bottom.
Water parameters:
Temp 42.4F
PH 7.6+ (API test kit top of it's range)
KH 143 ppm (I measure for dkh, and that's the conversion from 8, using an Elos test kit)
NH3 0
Ambient temperature got up to 16.2C/61F today, but it looks like there is another few days of freezing temperatures and maybe snow on the way.
I'm a little surprised at how high the PH/KH is because I only half filled the pond with well water last May, the other half with rain water. There has been enough rain and snow since then to completely displace what well water was used. I've never tested the water from snow. I guess that's next.
..and a picture of the pond today: