I did a Google search and this product shows up. However, on a couple of sites it did say that it was “discontinued.” One site stated the presence of mercury was an issue. You might try your own internet search.
This is an interesting question - I wasn't aware that Salt was any good for Koi's. I researched very quickly what it can do for Koi's and most of what I found so far is it helps with the overall health of the Koi's or fishes.
Salt can be beneficial to fish (not just koi) but it can also be harmful to the plants in your pond. You have to be careful with using it if your pond is planted. I personally don't use salt in my pond for that reason. We did have one fish that had a large wound on his head that we treated with a salt bath with great results, but we removed him from the pond and put the fish into the salted water for treatment.
Salt is used in koi ponds in order to protect them from the effects of nitrite and to supposedly protect them from various parasites.
It's not a practice I support.
There is no need for salt unless specifically treating for a certain issue.
Focus on good water quality instead.