Dishwasher salt is a particular grade of crystalline sodium chloride intended for use in dishwashers. Dishwasher salt is used for the same purpose as (and is very similar to) water softener salt, namely to regenerate ion exchange resins used to remove the hardness ions calcium and magnesium from water. Dishwasher salt is in a granular form, with particles larger than common table salt and unlike table salt has no added iodine (included as a dietary supplement in the U.S.). The granule size ensures that the salt dissolves slowly and that fine particles do not block the softener unit.
95% sodium chloride (salt), 5% other (Anticaking agent e.g. sodium ferrocyanide or potassium ferrocyanide)