ANSI/APSP/ICC-11 2019 the proper range in response to sanitizer addition, bather load, or other factors. With too little alkalinity there will not be enough buffering and the pH may quickly drift out of the proper range. At excessively high bicarbonate/carbonate alkalinity there will be a tendency for the pH of the water to drift upward, due to the rapid escape of carbon dioxide from the water into the air.
Low levels of calcium hardness are not as important for non-cement-based surfaces. Regardless of pool surface, it is important to keep the calcium concentration below the maximum to avoid production of scale and cloudy water. Pool water calcium hardness shall be maintained between a minimum of 150 ppm and a maximum of 1,000 ppm as CaCO3, and ideally between 200 ppm and 400 ppm. In spas, calcium hardness shall be maintained between a minimum of 100 ppm and a maximum of 800 ppm as CaCO3 and ideally between 150 ppm and 250 ppm. The lower calcium limit in spas is intended to offset the impact of temperature on water balance. It should be noted that the cold water present at startup of a spa requires special attention to ensure that the water is properly balanced.
With optimum buffering from total alkalinity, it is easier to maintain pH, swimmer comfort, sanitizer efficacy, water balance, and clarity.
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References
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The Association of Pool and Spa Professionals. APSP Service Tech Manual, 4th Ed. Alexandria, VA
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The Association of Pool and Spa Professionals. Chemical operational parameters. Alexandria, VA.
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Wojtowicz, J. A. Treatment of swimming pools, spas, and hot tubs. 1998. Kirk – Othmer Encyclopedia of Chemical Technology. 4th ed. vol. 25, pp. 569-594. New York: John Wiley and Sons, Inc. A7.4 — Total dissolved solids
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Total alkalinity shall be maintained between a minimum of 60 ppm and a maximum of 180 ppm as CaCO3 and ideally between 80 ppm and 100 ppm as CaCO3 where calcium hypochlorite, lithium hypochlorite, and sodium hypochlorite are used, because these sanitizers will cause the pH to rise. The ideal range where sodium dichlor, trichlor, chlorine gas, and bromine compounds are used is between 100 ppm and 120 ppm as CaCO3, because these sanitizers will cause the pH to fall. Certain sanitation systems such as PHMB are relatively unaffected by total alkalinity.
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The portion of the alkalinity coming from carbonate and bicarbonate also affects calcium carbonate saturation. (See Langelier Saturation Index.) The maintenance of calcium carbonate saturation also reduces the tendency of pool water to etch or scale plaster surfaces.
References
Total Dissolved Solids (TDS) is a measure of all dissolved ions in the water and may or may not indicate a problematic condition. The following will contribute to TDS: source water, rain water, treatment chemicals, and bather waste. As the water evaporates the solids remain behind and become more concentrated. High TDS levels (1500 ppm above the concentration at start up) may correlate with the presence of undesirable substances that may cause poor water quality and indicate the need for water replacement.
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The Association of Pool and Spa Professionals. APSP Service Tech Manual, 4th Ed. Alexandria, VA.
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The Association of Pool and Spa Professionals. Chemical operational parameters. Alexandria, VA.
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Wojtowicz, J. A. Treatment of swimming pools, spas, and hot tubs. 1998. Kirk – Othmer Encyclopedia of Chemical Technology. 4th ed. vol. 25, pp. 569-594. New York: John Wiley and Sons, Inc. Wojtowicz, J.A. 2001. The carbonate system in swimming pool water. Journal of the Swimming Pool and Spa Industry, vol. 3, no. 1, pp. 54-59.
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A maximum level for TDS is not given, because salt water pools intentionally have high concentrations of sodium chloride. The sodium chloride will contribute to TDS, but will not cause decreased sanitizer efficacy or cloudy water.
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A7.3 — Calcium hardness
TDS can decrease the efficacy of sanitizers if the dissolved ions include oxidizable materials, such as organics, that exert a chlorine demand. Water with a high TDS can be more aggressive (corrosive). High TDS can also accelerate galvanic corrosion of pool equipment. When calculating the Langelier Saturation Index (LSI) values, the TDS levels should be taken into consideration (see A7.5, LSI). Cloudy or hazy water is from total suspended solids (TSS) not TDS.
Maintenance of the Calcium Hardness in the recommended range helps to keep water balanced per the Langelier Saturation Index (LSI), influencing the water’s corrosiveness or tendency to scale, depending on the degree of calcium saturation. Total hardness is the measure of primarily calcium and magnesium combined. There are test kits for total hardness and others for calcium hardness. It is the calcium hardness that should be used in the LSI calculation. ©2018 The Association of Pool & Spa Professionals
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