Sodium Thiosulfate Uses In preparation of fixing baths Ingredient in various reducersNote:Hypo is available in two forms: anhydrous and, more commonly crystalline. Crystalline hypo, when dissolved, lowers the temperature of the water considerably, whereas anhydrous does not. Always begin with water of at least 90deg.F/32deg.C when mixing the crystalline form. Use 64% of the anhydrous salt as a substitute for crystalline hypo