OK, I was a little concerned when you said it was 20% potassium chloride. That sounds similar to the composition of Dowflake. Its a little higher in sodium chloride but that isn't a problem since its the major component in sea water. Make sure they give you a Material Safety Data Sheet with it and Technical Bulletin. Did they say if it was food grade?

This is basically the same thing that Kent sells as Turbo Calcium.

You might also want to try calling Chem Central. I think they are a distributor for Dow and would have Dow Flake.