RichToyBox,
thanks for everything. The fish are swimming around and look normal.
The water is clearing and that fat koi is now noticeably thinner.
Thanks again for your help, you saved my the fish.
Will still monitor ammonia for the next couple days.
Massive water change did the trick for now.
Bruce

Bruce,

If your water is not treated with chloramines, then massive water changes
will dilute the level significantly. Water treated with chloramines has
ammonia in it, so it becomes very hard to reduce the ammonia level with
water changes. If you can reduce pH to about 7.4, the ammonia becomes
non-toxic, but if your pond is like mine with a pH of around 8, it means
killing the carbonate hardness and the filter bacteria will suffer. In my
pond, it took about 3 or 4 days for the ammonia to be consumed by the
bacteria in the pond, but the nitrite spike took longer to get through.