The desired temperature for change of phase in a heat storage material rarely coincides with the melting point of a pure substance. It is, therefore, worthwhile to look for a method to adjust the melting temperature. This can be achieved by addition of a second salt. This second salt may or may not form solid solutions with the main component. In this paper we deal with an example for each case. Calcium chloride hexahydrate (CCH) forms solid solutions with calcium bromide hexahydrate, but not with potassium chloride. The influence of these two salts on the melting behavior of CCH is discussed.