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Pool Chemistry Explained


Free Chlorine vs. Combined Chlorine:The unpleasant smells and side effects often associated with chlorine are actually caused by combined chlorine (i.e., chloramines).Combined chlorine is a chlorine molecule that attacks a noxious particlein the water but is unable to destroy the noxious particle. This chlorine particle remains attached to the noxious particle until one of the two is burned off; hence the term Combined Chlorine (a.k.a. chloramines). To burn off the noxious particle and free up the chlorine again, pool owners have to shock (with chlorine) the pool periodically, but with the Natural Chlorine Generator, the noxious particles are burned off within the generator Cell and the combined chlorine is continuously converted back to free chlorine. The free chlorine level in the pool should be maintained at 2 to 4 ppm. This level of free chlorine is comfortable to swim in with no unpleasant smells, and maintains proper sanitizing power.

pH is a measure of the acidic or basic solution. A scale of 0 to 14 is used to measure pH. Pure water has a pH of seven (neutral), acid solutions have a pH of less than seven, and basic (alkali) solutions have a pH of more than seven. The recommended range is 7.2 to7.6; chlorine is much more effective within this range and the water is most comfortable for bathers.  pH levels above 7.8 drastically reduce the effectiveness of the chlorine. To lower the pH, add muriatic acid or dry acid. Be sure toread and follow the respective manufacturer’s instructions.

Total Alkalinity mitigates changes in pH. It is often referred to as the “big brother of pH.” Keeping proper levels of total alkalinity helps reduce unwanted fluctuations in pH levels. Total alkalinity is also used to offset high or low levels of calcium hardness. Add muriatic acid or dry acid to lower the total alkalinity and sodium bicarbonate to raise the total alkalinity. Be sure to read and follow the respective manufacturer’s instructions.

Stabilizer (Cyanuric Acid or Conditioner) is necessary in most outdoor pools to maintain appropriate levels of chlorine. Chlorine stabilizer helps provide an appropriate residual chlorine level in the water. Without stabilizer, UV radiation from the sun destroys most chlorine within 2 hours, but excessive amounts of stabilizer can decrease the effectiveness of chlorine. Chlorine stabilizer should be maintained at 60 ppm to offset the harmful effect of the sun while maintaining the effectiveness of the chlorine. Where pH/ORP automatic sensors are used, 40 ppm of stabilizer suffices.

Phosphates and Nitrates set very high demands on chlorine; most often nitrates and phosphates bring the chlorine level down to zero (0). You can have your water tested for nitrates and phosphates by the local pool professional.  Your pool should NOT contain Nitrates or Phosphates. To reduce Phosphate levels, use a phosphate remover from your local pool professional.To reduce Nitrate levels, the pool must be partially or fully drained. (Please check with your local pool professional prior to draining the pool).

Metals can cause loss of chlorine and can stain your pool. If a water test reveals the presence of metals, refer to your local pool professional for recommended methods of removal. Be sure to use a phosphate-free metal remover to avoid replacing a metal problem with a phosphate problem.

Calcium Hardness, like pH and alkalinity, affects the water tendency to be aggressive or scale forming. Lower levels of calcium hardness improve the chlorine generator ability to stay clean and provide softer silkier water for the swimmers. Check with your pool professional for proper calcium levels for your pool surface.

 Total Dissolved Solids (TDS)is a measure of many types of dissolved materials, including salt. High effective TDS levels (i.e., 1500 ppm and up) cause cloudy water and significantly increase chlorine demand. To obtain the effective TDS level in a pool using a salt system, subtract the salt level from the TDS reading. (e.g., 5000 TDS – 4000 Salt= 1000 effective TDS).

 Saturation Index determines whether the pool water is balanced, aggressive, or scale forming by comprehensively taking into account all the relevant factors, including pH level, alkalinity level, calcium hardness, and temperature. These factors should be tested periodically, and then included into the worksheet on the following page to verify theproper balance of the pool and make adjustments as necessary.


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