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Parks & Rec Business
| Testing The Waters Keep it Simple Swimming pool water chemistry can seem overwhelming to the aquatic professional when chemical terminology and treatments are thrown into the mix of “keeping your pool safe and clean.” Over the years I have accumulated enough chemistry textbooks, chemical treatments, articles and manufacturer’s pool care guides to fill up two shelves in my library. How can I make this complicated topic easy for the aquatic manager? There are variables based on the environment, for example, indoor or outdoor facility, pool usage and bather load. Keeping it simple means it’s easier to manage the pool on a daily basis. The primary goal of every aquatic facility manager is to provide a safe environment for those who get in the water, to prevent recreational water illnesses and contamination, and to maintain a water condition that will insure user comfort. In addition, there is the responsibility to protect the equipment and pool surfaces. This study of basic swimming pool and spa water chemistry will be broken into two main topics, Disinfection and Water Balance. Disinfection is the destruction of pathogenic and other kinds of microorganisms by physical or chemical means. Disinfectants are chemical substances used to destroy viruses and microbes (germs), such as bacteria and fungi. The ideal disinfectant offers complete sterilization without harming other forms of life, and be inexpensive and non-corrosive. Unfortunately, ideal disinfectants do not exist. Many disinfectants are only able to partially sterilize. ... en.wikipedia.org/wiki/Disinfection In swimming pool applications, the major disinfectant used is chlorine, which is introduced into the pool water through several compounds by various methods. When added to water, chlorine produces hypochlorous acid, the hypochlorite ion, hydrogen ion and a by-product specific to the type of chlorine. Slide: Courtesy of National Swimming Pool Foundation® If sodium hypochlorite is being used, the by-product is sodium. If calcium hypochlorite is being used, the by-product is calcium. There is a direct relationship between the percentage of active hypochlorous acid and pH of the water. The slide below illustrates the active percentage of HOCl. As the pH increases, the active HOCl decreases. Free chlorine is actually the sum of hypochlorous acid and hypochlorite ion. Active chlorine vs. pH at 86 degrees F (R.W. Lowry, “Pool Chlorination Facts”) Getting back to the goal of keeping this topic simple, one must understand the relationship between pH and chlorine. Keeping the pH between 7.2 and 7.8, with an ideal range of 7.4 to 7.6, will insure stable free chlorine residual. As the free chlorine reacts with nitrogen compounds or organics (germs, bacteria, ammonia, body fluids, body wastes, algae), combined chlorine is formed. Another term for this combination is “chloramines.” This is the chlorine smell experienced in some swimming pool environments. The goal of the aquatic manager is to have zero chloramines in the water. The elimination of these chloramines can be achieved by adding sufficient free chlorine to the pool water to break up the chloramines, release the ammonia into the atmosphere, and return the chlorine to a free state so it can “kill more germs>” Opinions differ on this breakpoint process. I recommend that you test a water sample for total chlorine residual, subtract free chlorine residual, and the difference will be combined chlorine (CC=TC-FC). Once this combined chlorine is determined, multiply the combined by 10. This will be the amount of chlorine ppm you will need to increase the chlorine residual in the pool water in order to achieve breakpoint. It is important to understand the characteristics of chlorine compounds and what impact they have on the overall water balance. In the chart below, liquid chlorine (bleach) has a pH of 13, which indicates that as this liquid is added, the pH of the pool water will increase. Conversely, if tri-chlor tablets, with a pH of 3.0, are used, the pool water pH will inherently decrease. Water Balance In order for the disinfectant to work at peak performance, the water must be balanced. There are five major balancing factors which must be tested and adjusted in the swimming pool environment to eliminate corrosion, surface staining, eye and skin irritation, cloudy water, clogged filters and etching of pool surfaces. These major factors are pH, total alkalinity, calcium hardness, total dissolved solids and temperature. pH and Total Alkalinity Most pool chemistry courses start with pH. I believe that total alkalinity should be addressed and adjusted first. Total alkalinity is the measure of the ability of water to resist changes in pH. I like to call TA Big Brother, who looks after and protects his little sister, pH. If the pH readings fluctuate, the total alkalinity is out of balance. The rule is to maintain the total alkalinity between 80 and 120 ppm. To increase total alkalinity, bicarbonate of soda is primarily added. To decrease, most operators use muriatic acid. The pH (“power of hydrogen”) scale measures the acidity or alkaline (base) of the pool water and influences how the water impacts bather comfort. Many factors affect pH: acid rain, swimmer perspiration, wind and aeration, as well as the type of disinfectant being introduced. To raise pH, the operator must add sodium carbonate or soda ash. To lower pH, muriatic acid or sodium bisulfate is used. More public pools are leaning toward carbon dioxide gas, which lowers pH but has a tendency to raise total alkalinity. Whatever method is used, the outside range for pH is 7.2 to 7.8, with an ideal range of 7.4 to 7.6. Calcium Hardness Water is considered the universal solvent. If there are not enough minerals, primarily calcium and magnesium in the pool water, it will “pull these minerals out of the pool surface.” This is a major reason tile falls off the pool. The thinset used to set tile has calcium in its composition. If there is not enough calcium in the pool water, it will pull the calcium from behind the tile and cause the tile to fall. In addition, the pool surface will begin to feel sandy, and bathers will complain about roughness on their feet. The advisable range for calcium hardness is 200 to 400 ppm. To increase calcium, calcium chloride should be added. Some chemicals are designed to decrease calcium, but most pool operators still use the dilution method, lowering the water level and adding fresh water to the pool. Calcium is very soluble in cold water. You may notice, as the temperature of the water increases, the water may become cloudier; the calcium comes out of solution and creates a cloudy haze. Total Dissolved Solids Total dissolved solids (TDS) is the total weight of all soluble matter in the water, and is measured by its electrical conductivity. Pool balancing chemicals, evaporation, clarifiers, deformers, enzymes, tile cleaners, salt, bather waste and algicides all add to the TDS. The age of the pool, without draining and refilling, increases the TDS. I call this phenomenon “tired water.” As the TDS increase, they impede the disinfection process and increase the possibility for algae and bacteria growth. Temperature The temperature of the water also impacts the water balance: the higher the water temperature, the more scaling occurs, the lower the water temperature the more corrosive. I recommend a professional test kit for the following: free chlorine, total chlorine (some now test combined chlorine), pH, total alkalinity, calcium hardness and cyanuric acid. There are also various testing procedures and equipment available to check for TDS levels. Now that we can test for these factors, the final step is an easy conversion and calculation, called the Saturation Index. This index shows whether the pool water is corrosive or scale forming, and can identify major problems early by determining whether the pool water will deposit calcium carbonate or maintain it in solution. Saturation Index = pH + CF + AF + TF – TDSF (12.1) Saturation Index = pH + Calcium Factor + Alkalinity Factor + Temperature Factor – TDS factor • Saturation index = 0 (water is perfectly balanced) • Saturation index = negative number (may cause corrosion) • Saturation index = positive number (may form scale) Total Dissolved Factor If TDS is less than 1,000 ppm, subtract 12.1 If TDS is greater than 1,000 ppm, subtract 12.2 Keys to Easy Water Chemistry • Use a professional test kit with fresh reagents. Follow the manufacturer’s instructions and monitor expiration dates. • Test water from the midpoint of the pool, at least 18” below the water surface, away from inlets. • Know the characteristics of your sanitizer (disinfectant). Maintain chlorine levels according to local health codes or standards. Test for combined chlorine and add chlorine to reach breakpoint chlorination. • Test all water-balance factors. • Maintain total alkalinity (TA) 80 to 120 ppm (adjust before pH). If disinfectant has a low pH, keep TA 100 to 120. If disinfectant has a high pH, maintain TA 80 to 100. • Maintain calcium hardness 200 to 400 ppm. • Maintain cyanuric acid 30 to 50 ppm in an outdoor pool environment. Cyanuric acid (stabilizer) is not necessary in indoor pools. • Test for total dissolved solids. Watch for tired, dull water. • Calculate the Saturation Index at least once a week. Watch for slight deviations and access the reason for change. • Adjust chemicals when necessary. • Never add chemicals when bathers are present and in the water. • Follow chemical addition instructions from the manufacturer’s labels. • Maintain Material Safety Data Sheets on all chemicals. • Keep chemical safety equipment and spill kits available, and train all staff on emergency procedures. Sidebar References www.eProAcademy.org, an online training center eProAcademy™ offers online courses in occupational safety, employment law, healthcare, environmental and hazardous waste management, and DOT training for drivers of hazmat shipments. The courses are designed by experts in online training and stringent federal, state and company requirements, including chlorine safety, compressed gas safety, hazard communications and more. Log onto http://www.eProAcademy.org. The Pool Math Workbook from NSPF, www.nspf.org Sidebar Sidebar #1 For those looking to achieve a college degree program in the aquatics field, the Keiser University Associate of Science Aquatic Engineering Degree offers a two-year program, consisting of 60 semester hours that are achieved exclusively online Each student is required to complete 36 credit hours of major courses and 24 credit hours of general education courses. The program encourages students to broaden their knowledge in all aspects of swimming pool and spa management and operation. The online feature makes the degree program available to the national and international community of pool and spa professionals, and those seeing employment in the field. The online format enables schedule flexibility and increased access to those currently employed. For more information about the Aquatic Engineering degree at Keiser University, visit www.keiseruniversity.edu and click on “Online Education,” or call 866-535-7371, or e-mail ccentrella@keiseruniversity.edu and request a brochure. About the author Connie Gibson Centrella is Program Director for the online Aquatic Engineering Program at Keiser University eCampus. She was recently honored with the Evelyn C. Keiser Teaching Excellence Award “Instructor of Distinction.” Ms. 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. |
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