Water hardness, alkalinity

Total Alkalinity and Calcium Hardness These two factors must be considered together, because one influences the other. Temperature, pH, total alkalinity and calcium hardness are four major factors used to calculate the Saturation Index, which is a measure of water’s tendency to scale or corrode surfaces that it touches. The Saturation Index must...

Total Alkalinity and Calcium Hardness These two factors must be considered together, because one influences the other. Temperature, pH, total alkalinity and calcium hardness are four major factors used to calculate the Saturation Index, which is a measure of water’s tendency to scale or corrode surfaces that it touches. The Saturation Index must be considered in picking a target for total alkalinity and calcium hardness. But in pools maintained between 25.5°C and 29.5°C and at pH levels of 7.4 to 7.6, temperature and pH can effectively be considered constants, not variables. This somewhat simplifies calculating the Saturation Index. TOTAL ALKALINITY should generally be between 50 and 125 ppm and calcium hardness between 200 and 500 ppm. To ensure these factors’ levels fall within the appropriate range, total alkalinity times calcium hardness in ppm should approximately equal the number 25,000 (+/- 10%) For instance, if total alkalinity is 50 ppm, calcium hardness should be about 500. Note that this 25,000 rule only works if the pH is between 7.4 and 7.6 and the temperature is between 25.5°C and 29.5°C. Makeup water characteristics, bath load and chemicals used affect precisely where in this total alkalinity and calcium hardness range a pool is operated. Under normal operations, total alkalinity tends to drop in most pools because it is reduced by gas chlorine feed and hydrochloric acid (or pH Minus) feed. To counter these constantly declining levels, total alkalinity’s lower levels should be maintained between 50 and 80 ppm and countered with higher calcium hardness. If total alkalinity falls below 50 ppm, operators can feed calcium chloride at the appropriate dosage to achieve a calcium hardness level that satisfies the 25,000 rule. TREATMENT: If the total alkalinity is below 50 ppm, asdd SODIUM BICARBONATE (noit Soda Ash) or Magnesium Oxide (MgO, PH Flats). Standard dosage: Sodium bicarbonate - 6kg per month per 100 M3 of water Magnesium oxide - 2kg per month per 100 M3 of water CALCIUM HARDNESS, on the other hand, is a comparatively stable factor in pool water chemistry. If total alkalinity falls below 50 ppm, operators can feed calcium chloride at the appropriate dosage to achieve a calcium hardness level that satisfies the 25,000 rule. New pools that have fresh plaster, grout or concrete can be maintained at a Saturation Index level closer to 30,000 or 35,000 for the first six to 12 months while the surface finish is still new.