definitely there does not exist a sodiumthiosulfate-hexahydrate ( x 6 H2O), only a pentahydrate (x 5 H2O) and the anhydrous form. I'm a chemist and I have read many old and new books about photographic formulations, I never found a hexahydrate. Also in books about inorganic chemistry and in chemical encyclopedias you'll only find the pentahydrate and the anhydrous hypo. This is an error.