Strategies For A Healthy Pool

By Connie Sue Centrella
Photo Courtesy of National Swimming Pool Foundation

Providing a safe, healthy, disease-free swimming environment can be an overwhelming task for any operator. And without a full understanding of water-chemistry basics, the task will be difficult and next to impossible.

Recreational Water Illnesses (RWIs) are brought into the pool by bathers who do not shower or those who utilize poor hygiene. These RWIs can be contracted by swallowing the pool water, or by penetrating the skin, or just by breathing the vapors (mists) above the water’s surface. Encouraging healthy behaviors before entering the pool will help. For example, facilities should require and enforce showering before entering the pool; swimmers should also be discouraged from urinating in the pool, since the combination of urine and chlorine is dangerous;  the Centers for Disease Control’s (CDC) Six Pleas should be widely posted, urging people who are ill with diarrhea to not swim (see sidebar). These are three important steps for any aquatic facility to follow.

Swimming pools and spas can be a breeding ground for bacteria if the operator does not maintain a constant halogen (chlorine/bromine) residual. It is critical to diligently monitor the pool chemistry parameters. There are two strategies to provide superior water care:

  • Maintain free halogen level to kill harmful bacteria and viruses
  • Maintain proper water balance.

In an effort to ward off bacterial infections, aquatic operators must be precise in maintaining disinfectant levels. Most state and local codes insist on a free chlorine residual of 1.0 parts per million (ppm) to 5.0 ppm for pools, and 3.0 ppm to 10.0 ppm for spas. In addition, there are specific recommendations from the CDC in case of a fecal accident in the pool. (

Chlorine—Free, Combined, And Total
Chlorine is the most common disinfectant, and may be introduced into the pool water through various methods. Most codes require a constant feed apparatus, such as a feed pump or erosion-type feeder. The most common chlorine compounds used in pool operation are sodium hypochlorite (liquid), calcium hypochlorite (granular or tablet), and trichlor (tablet form). Each chlorine type has different reactions in pool water, but all are excellent in killing bacteria if the chlorine level is within the proper range. When added to pool water, the chemical effects of these compounds break down to form hypochlorous acid, which is the active killing form. There is a by-product produced, though, depending on the chlorine compound. For instance, the by-product of sodium hypochlorite is sodium, and the by-product of calcium hypochlorite is calcium. These by-products also impact water chemistry as high calcium increases calcium hardness, which may cause cloudiness.

As the free chlorine (hypochlorous acid, also referred to as HCOI) reacts with organic compounds (germs, bacteria, ammonia, bodily fluids, bodily waste, and algae), it forms combined chlorine. Another term for this is chloramines. These render a strong chlorine odor, can cause eye and skin irritations, and create disinfection by-products (DPBs) that can negatively impact the health of those who frequent the facility. Traditional procedures require testing for the free chlorine and the total chlorine, the difference being the combined chlorine residual. (TC-FC=CC).

Operators should test for the free and total chorine frequently, as it is important to eliminate the combined chlorine in the pool. Standard practice dictates that when the combined chlorine is greater than 0.2 ppm, a shock treatment known as breakpoint chlorination must be implemented. The ultimate goal of the operator is 0.0 chloramines in the pool water.

The active level of hypochlorous acid (free chlorine) is dependent upon the pH of the pool water. The higher the pH, the less active the HOCl is. For instance, at a pH of 8.0, only 24 percent of HOCl is active; conversely, at a pH of 7.2, HOCl is 66 percent active. The ideal range of pH for bather comfort is 7.4 to 7.6.

Five Factors Affect Water Balance
In order for the chlorine to work effectively in pool water, it is vital that water balance is addressed. There are five major balancing factors that need to be tested on a regular basis in order to calculate a standard called the saturation index (SI): pH, total alkalinity, calcium hardness, temperature, and total dissolved solids (TDS).

The pH is the measurement of how acidic or alkaline the water is. The testing of pH is mandatory by most codes. Environmental factors that affect pH are rain and wind, as well as swimmer wastes, such as perspiration and urine. pH also influences bather comfort. Burning of eyes, corrosion of surfaces, and standing of surface walls are the result of low pH.  Conversely, high pH will produce cloudy water as well as chlorine inefficiency. To increase pH, most operators use calcium carbonate (soda ash); to decrease pH, some type of acid must be introduced, either muriatic or sulfuric acid (liquid form) or sodium bisulfate (dry acid).

Total Alkalinity
Total alkalinity is the measure of the ability of water to resist a change in pH. It keeps the pH stable. Total alkalinity should be monitored at least weekly. The rule is to maintain total alkalinity between 80 ppm and 120 ppm. Experience shows that, if a chlorine compound with a high pH, such as sodium hypochlorite or calcium hypochlorite, is used, total alkalinity should be kept between 80 ppm and 100 ppm. If the chlorine compound with a low pH, such as trichlor, is used, total alkalinity should be kept between 100 ppm and 120 ppm.

Calcium Hardness
Calcium-hardness testing is required to measure the minerals in the pool water. Low calcium can cause rough surfaces (a sandy-rough feeling on the feet), and high calcium can form scale on the pool surfaces as well as inside the pool piping. The ideal parameter for calcium hardness is 200 ppm to 400 ppm. In hot water environments such as spas and hot tubs, it is recommended to maintain a lower calcium-hardness level (150 ppm to 250 ppm). This is because calcium is more soluble in cold water. Operators will notice that as the water temperature increases in the summer months, the water may become cloudy; calcium comes out of solution in warm water, which creates a cloudy haze.

Just as high calcium increases high saturation, so does temperature. Temperature impacts the water balance--the higher the water temperature, the more scaling will occur. Lower temperatures create more corrosion. Operators in colder climates, especially in winter, should monitor the saturation index even if no one is using the pool. As the water gets colder, a corrosive condition will be created and damage the pool surface.

Total Dissolved Solids
Total dissolved solids (TDS) is the sum of all solids (chemical treatments) introduced into the pool water. The solids dissolved must be measured with a digital-type reader to determine conductivity.  Some examples of chemical treatments that increase TDS are balancing chemicals, clarifiers, defoamers, enzymes, tile cleaners, bather waster, and algaecides.

Regular Testing Catches Problems Early
A professional test kit is mandatory for aquatic facilities to assess these parameters. Once the pH, total alkalinity, calcium hardness, temperature, and total dissolved solids are measured, an easy conversion can be made to determine a saturation index (SI) that will indicate if the pool water is corrosive or scale-forming. This is the best way to identify pool-water problems early and respond before major damage occurs.

Strategies for a healthy pool begin with knowledge and understanding of basic pool water-chemistry parameters. It is not complicated, yet it takes the active engagement of the operator on a daily basis to test the pool, add necessary chemicals to maintain water balance, and make a commitment to be proactive instead of reactive in pool-water management.

Connie Sue Centrella is a professor and Program Director for the online Aquatic Engineering Program at KeiserUniversity eCampus. She is a five-time recipient of the Evelyn C. Keiser Teaching Excellence Award “Instructor of Distinction.” Centrella is an industry veteran with over 40 years experience in the pool and spa industry. She is a former pool builder with extensive knowledge in pool construction and equipment installation, as well as manufacturing.