Check the listing for details. liquid reagents for Pool Lab - PoolWaterLAB - Water Tester - Kit to Measure Tota. Condition: New. Listed at 33.35 USD. (POL2010TH12) Hardness | 0.0 - 500.0 mg/l (ppm) | reagent for measurements - Total hardness. The shelf life of liquid reagents is 6 months. Basically dissolved salts belonging to the alkaline earth elements calcium and magnesium are found in non-distilled water. In rare cases, strontium and barium can also be found. These combine with carbonate ions to form water- insoluble compounds (calcium). Through the total hardness measurement, the potential danger of calcium precipitation is measured as the required carbonate ions form from hydrogen carbonate ions when water heats up or when there are pH values that are greater than 8.2 (comp. Alkalinity). When measuring calcium hardness (SVZ1300 tablet process), only the part of the dissolved calcium in water is measured. The amount of magnesium dissolved in water is determined from the difference between the measurement and the total hardness.