Source of Magnesium Chloride: You can get natural Nigari which is mainly Magnesium Chloride plus trace minerals. It is what is left after the Sodium Chloride is removed from sea water. Used a coagulant for making Tofu. You can order it from GEM Cultures ( www.gemcultures.com ) cost is $8.00 for 12 oz. or $21.50 for 4 lbs postpaid. This is a very small business so please consider this fact when ordering. They only accept money Orders and Checks mailed to them by snail mail.