Pool Chemistry is Essential
This article was published in the Houston Daily Journal on June 22, 2007.
One of the most important aspects of pool operation and maintenance is pool chemistry. According to the Consumer Product Safety Commission, there were over 2500 water-borne illnesses reported in 2005. The most common was Cryptosporidium. There were 61 people hospitalized and 8 deaths in the U.S. alone. Pool operation bares a heavy responsibility in the prevention of water-borne illness. There are five essential parameters of pool chemistry that must be observed to achieve adequate disinfection of algae and bacteria. They are disinfectant, pH, alkalinity, calcium hardness and cyanuric acid (commonly called stabilizer and found in outdoor pools).
Maintenance of free available chlorine (disinfectant) is a top priority in pool disinfection. This is chlorine dissolved in water that is negatively charged and actively trying to bond with positively charged particles, such as algae or bacteria. These levels should be maintained between 1.5 part per million to 3.0 ppm.
Most of the common chlorines that are added to a pool have a pH of between 10-14 and cause the pH to rise. The higher the pH gets the less active the chlorine is. When pH is low, the chlorine is more active but can cause skin and eye irritation. It is for these reasons, the pH should be maintained between 7.2 and 7.8 at all times.
Total alkalinity is the total concentration of bases in water expressed as parts per million (ppm) or milligrams per liter (mgl) of calcium. These bases are usually bicarbonates (HCO3) and carbonates (CO3), and they act as a buffer system that prevents drastic changes in pH. For example, in waters with low alkalinity, pH might fluctuate from 6 or lower to as high as 10 or above; while in high alkalinity waters, pH might fluctuate from about 7.5 to 8.5. It is important to maintain the proper alkalinity levels of 80-100 ppm in order to more easily control pH. If alkalinity is too high you have staining, scale and difficulty adjusting pH. When it is low, corrosion is possible and pH fluctuates. Alkalinity should always be corrected first before correcting pH.
Calcium hardness is another important aspect. Calcium levels should be maintained between 200-400 ppm. If there is too much, cloudy water and scaling can occur. If it is too low damage to equipment, metals, concrete and tile will occur. If proper calcium levels are not maintained the implications to decks and plumbing can be disastrous and expensive. It is usually corrected easily and once corrected doesn’t have to be closely watched like the disinfectant, pH or alkalinity.
Finally, stabilizer or cyanuric acid is another important aspect of pool maintenance. Up to 97% of free chlorine (sanitizer) can be lost in sunlight within 2 hours when the proper levels of stabilizer are not maintained. Optimal levels are 30-50 ppm. Because most chlorine has stabilizer as an additive, the levels of cyanuric acid will rise over the years. These levels should not be allowed to exceed 100 ppm. High cyanuric acid levels reduce the free chlorine’s ability to chemically bond and disinfect. The only way to lower these levels is to dump the pool and refill with fresh water.
Each person that enters a pool adds approximately 1.4 grams of fecal matter as well as urine, saliva, perspiration and other nitrogenous waste. These elements when left unchecked can possibly be deadly. Routinely test your pool water and frequently super chlorinate or “shock” a pool, especially after the bather load has been high. If anyone has any questions regarding pool operation and maintenance, they are welcome to call me at my office (478) 218-2020.
Submitted by Robert A Morgan
Environmental Health Specialist II
Houston County Health Department