Moving Koi to a newly constructed concrete pond may trigger Koi spawning. It happened to me on two occasions.
I believe it has to do with the sudden PH level change. In a matured pond, the PH level is probably near 7 (neutral) or slightly above 7 (slightly alkaline), with buffering provided by the cockle shells in my filter. In my newly constructed concrete pond, the PH is probably higher due to some leaching of cement into the water. This may trigger the Koi to spawn soon after they are transported from my old pond into my newly constructed pond.
the first time it happened, none of the eggs released hatched. They just turned white and is soon eaten by the Koi. The second time it happened (in my third Koi pond), some of the eggs actually hatched. I counted about 6 to 7 fries (2 to 3 mm long) hiding and living in my filter. I did not remove them from the filter and main pond. Amazingly, one fry manage to survive! It is about 1 year old now (smallest Koi in the photo below).
