Update: That one koi did survive...a butterfly koi, incidentally. This is the only koi that never comes up to feed on pellets. Interesting, I think. I never did hear back from Petsmart. I will still be contacting them again though.
I did have the water tested from the pond, the well water that feeds fresh water into the pond, and my house well water (the house b/c I did a goldfish experiment w/ the food). ALL the water tests came out perfect. So I purchased 4 "test subjects".
I bought 4 active goldfish ( from 2 tanks and were 2 different sizes) and fed them the koi food in question. One died within 24 hours, one died the day after that. The other two lasted a week, looked healthy so I put them in the koi pond:after 7 days in a fishbowl w/ observation. They did fine until they disappeared several days later. (yikes)
So, it's hard to say..maybe there is something mixed in the food unevenly? The goldfish only got about 3 pellets total per day (due to size of fish and food).
Tomorrow I plan on investing in some 10" koi (but worried about the invesment b/c of the size of these new koi is perfect for predators). But I just can't afford the larger size.
I miss my beautiful koi.