ریحنت ست سختی هک Hardness (ULR) Reagent Set, Solution Pillows Reagent set ultra low range hardness determination by the Chlorophosphonazo method. Hach Method 8374. Range: 4 - 1000 ug/L Ca & Mg as CaCO3. Chlorophosphonazo reagent solution is packaged in unit-dose solution pillows. (100 tests).