Hardness (calcium): The EGTA method is specific for calcium hardness. The EGTA titrant in alkaline solution is employed with a zincon indicator. Results are expressed as ppm (mg/L) CaCO3. Shelf-life: eight months. Although the reagent itself is stable, the end point indicator has a limited shelf-life. We recommend stocking quantities that will be used within seven months. Hardness (total): The total hardness method is applicable to drinking, surface, boiler, and brine waters. The EDTA titrant is employed in alkaline solution with a calmagite indicator. This method determines the combined calcium and magnesium concentration of a sample. If no magnesium is present, the end point of the titration normally appears sluggish. However, the reagent has been specially formulated to ensure a sharp end point regardless of the presence of magnesium. Results are expressed as ppm (mg/L) CaCO3.