Swimming Pool Service Technician's Study Guide This Study Guide was provided courtesy of Los Angeles County - Department of Health Services Environment Health Recreational Health Program DISINFECTION The pH or acidity/alkalinity of pool water plays an important part in determining the effectiveness of chlorine products at disinfecting pool water. When chlorine is added to pool water, it results in formation hypochlorous acid, the major disinfecting agent of all chlorine compounds. Cl + H²0 » HOCl + HCl In the above equation, when chlorine gas is added to water it forms Hypochlorous Acid and Hydrochloric Acid. Hypochlorous Acid is measured as free available chlorine residual. Hydrochloric acid is a by product and is not an effective disinfectant. Depending on the pH, Hypochlorous Acid disassociates into hydrogen ions and hypochlorite anions. HOCl « » H+ + OCl- Hypochlorous Acid will disassociate or breakdown into hydrogen ions and hypochlorite anions depending on the pH of the water. The lower the pH or more acidic, the more Hypochlorous Acid remains in the water and the more disinfection takes place. The higher the pH the less hypochlorous acid remains and more hydrogen ions and hypochlorite ions exist. Hypochlorite anions are a weak disinfectant. Chlorine tends to combine with ammonia products and other nitrogen compounds in pool water to form chloramines which are measured as combined chlorine. NH3 + HOCl » NH2Cl + H20 This equation shows ammonia combining with Hypochlorous Acid to form Monochloramine plus water. Further chemical reactions can form additional chloramines such as Dichloramines and Nitrogen Trichloride. Monochloramines are the most prevalent type of chloramine in pool water. Combined chlorine is a weak disinfectant which imparts a strong chlorine odor and irritates the eyes. Combined chlorine forms more rapidly during heavy bather loads. The ideal level for combined chlorine is 0. When the combined chlorine level exceeds 0.2 - 0.5 parts per million (ppm), the pool should be superchlorinated or shocked. This is usually accomplished by increasing the chlorine residual to 5 - 10 ppm. Doing so achieves breakpoint chlorination which is the process of adding sufficient free chlorine to convert combined chlorine or chloramines to inert elements. The State Pool Code requires that the free available chlorine level in pool water be maintained at 1.0 ppm or above in pools not using stabilizer and 1.5 ppm in pools that use stabilizers. The Health Department recommends maintaining chlorine residuals in swimming pools at 1.5 to 2.5 ppm and spas at 2 - 3 ppm. Pools that have been superchlorinated should not be used until the chlorine residual reduces below 5 ppm. Bromine in its elemental form is a reddish-brown liquid approximately three times heavier than water. It is extremely dangerous to handle. Safer forms of bromine have been developed such as Hydantoin bromine which come in sticks or tablets and can be used in an erosion-type feeder. Bromine has several advantages over chlorine. Bromamines are excellent disinfectants and unlike chloramines do produce an objectionable odor and eye irritation. Bromine is a more effective disinfectant across a wider pH range than chlorine. Bromine must be dispensed in a device called a brominator which operates similar to an erosion type chlorinator. Bromine levels in swimming pools and spas should be kept between 3.5 - 4.5 ppm and 4.5 - 5.5 ppm in spas. It's main disadvantage is it's high cost. There are basically two chemicals which are commonly used to test for chlorine residual in pool water. The first is Orthotolidine ( OTO). Its disadvantage is that unless performed under special conditions, it cannot accurately measure free chlorine and combined chlorine but instead indicates only total chlorine residual. Test kits using DPD ( Diethyl-p-phenylene-diamine) on the other hand, can measure both free chlorine and combined chlorine levels and are the only type that can be used on public pools. A common type of DPD test kit adds a number 1 tablet to a measured amount of pool water to obtain a free chlorine residual reading by comparing the color of the water to standard color blocks. A number 3 tablet is then added to obtain the total chlorine residual. The combined chlorine residual can be calculated by subtracting the free chlorine residual from the total chlorine residual. For example, if a pool has 3.0 ppm of total chlorine and 2.0 ppm free chlorine ,the amount of combined chlorine will be 1.0 ppm. Water for the test should be taken between 12 to 18 inches below the surface of the water. Orthotolidine or DPD tablets should never be dropped directly into the water as the results will be inaccurate and introduction of chemicals to the water that could be hazardous to bathers. Water from tests should not be thrown back into the pool. Directions which come with the test kit should be carefully followed. Liquid chlorine os Sodium Hypochlorite ( NaOCl) has approximately 10 - 12% available chlorine and a pH of 13+. Regular use of liquid chlorine requires the addition of an acid product to control pH. It takes approximately 8 ounces of acid to neutralize the caustic nature of one gallon of liquid chlorine. The advantages of using Sodium Hypochlorite is low cost, minimal danger in use and storage, and ease in mixxing with pool water. The disadvantages are short shelf-life, increased levels of salt (sodium) in pool water, and possibility of scale formation if pH is not controlled. Trichlorisocyanurates and Dichlorisocyanurates ( Trichlor & Dichlor) are organic chlorine compounds which have chlorine molecules attached to a molecule of Cyanuric Acid. Both compounds are acidic, with Trichlor having a pH of 2 to 3 and Dichlor a pH of 6.8. Soda ash is usually added to raise the pH when these products are used. Trichlor has 90% available chlorine and Dichlor 60-65%. Gas chlorine (Cl2) has 100% available chlorine. It is a light green gas which is 2½ times heavier than air. It is extremely toxic and can be used at public pools only under strict conditions specified in the State Pool Code, including a separate chlorination room with proper ventilation and approved equipment. Cylinders, both full and empty, should ne secured to walls and stored in a separate chlorination room. Small leaks of gas chlorine can be detected with a 26 Baume solution of ammonia which will produce a white smoke. Large leaks should be approached with only an approved self-contained breathing apparatus. When chlorine gas dissolves in water it imparts an extremely low pH. It is necessary to continually feed soda ash or caustic soda to maintain the pH in balance. The advantages of using gas chlorine are low cost, indefinite shelf life, and its ability to oxidize and disinfect. The disadvantages are the dangers of handling the product, initial cost and upkeep of equipment, and special on-going training required. Calcium Hypochlorite (cal-hypo) (CA[OCl]2) is a dry and stable chlorine product with 65% available chlorine. The product is alkaline and requires addition of acid to balance the pH. The disadvantages of using calcium hypochlorite is it increases calcium hardness in the pool and it must be pre-mixed before adding it to pool water. Lithium Hypochlorite (LiOCl) is a dry and stable compound commercially available at 35% available chlorine and has an alkaline pH. It is often used to superchlorinate a pool. The disadvantages are high cost and relative short shelf-life at high temperatures. Chlorine products are strong oxidizers. they should never be mixed with one another, with solvents or other chemicals. Mixing inorganic chlorine with any of the organic chlorine products will likely result in a violent explosion. Mixing any type of acid with a chlorine product will result in formation of chlorine gas. All containers , vessels, and vats containing chemical products should be labeled properly. In order to prevent chlorine from dissipating from sunlight, Cyanuric acid or stabilizer is used in pools. This product which is slightly acidic, bonds the chlorine molecule until it is needed to be released for disinfecting. The level of stabilizer should be maintained between 40 - 60 ppm in pool water. Levels below 25 ppm are ineffective, and higher than recommended levels are not cost effective. State Law requires that Cyanuric Acid be kept below 100 ppm at all times in public pools. It is best to add Cyanuric Acid through the skimmer. The filters should not be backwashed for several days since Cyanuric Acid dissolves very slowly. Cyanuric Acid id=s usually added or adjusted several times a year. Both Dichlor and Trichlor chlorine products contain over 50% Cyanuric Acid and will replace lost stabilizer which occurs when pools are refilled after splash-out. Frequent use of stabilized chlorine can lead to excessive levels of stabilizer. The only way to reduce high levels of stabilizers is to partially drain and refill the pool. Automatic chlorinators are devices which dispense a small amount of chlorine into the recirculation system over a period of time, usually by pumping from a reservoir with a positive displacement type pump or through an erosion-type feeder. The reservoir type has either liquid chlorine or another diluted chlorine product in a 20 or 30 gallon reservoir. A positive displacement pump connected to a timer then pumps the liquid solution directly into the recirculation system. Erosion-type chlorinators are attached to the recirculation system at two points with different pressure levels. This causes recirculation water to flow into the chlorinator past chlorine tablets which slowly dissolve and introduces the chlorine product into the recirculation system. All public pools are required to have an automatic chlorinator. Floating type chlorinators or tablets placed in the skimmer are not permitted in public pools. Chlorinators should be periodically taken apart and cleaned with dilute muriatic acid. WATER BALANCE The pH of pool water is a measurement of it's hydrogen ion content or acidity / alkalinity level. The pH range can extend from 0 to 14. At a pH of 7 the water is neutral and neither acidic or alkaline. As the pH is lowered towards 0, the water becomes more acidic. As the pH is raised towards 14 the water becomes more basic or alkaline. A change in pH from 7 to 5 represents a 100 fold increase in hydrogen ion concentration or acidity. The pH of pool water should be kept between 7.2 and 8.0. It is important to maintain pH at proper ranges because the effectiveness of chlorine as a disinfectant is dependant on proper pH levels. The pH of pool water is normally measured using a chemical called Phenol Red, which has an indicator range of 6.8 to 8.0. A drop or two of Sodium Thiosulfate is added to the test to eliminate any residual chlorine which will interfere with the test. The dropper bottle should be held in a vertical position when dispensing the drops and the hand should not be used to cover the test vial when mixing as this may produce false readings. Various chemicals are used to adjust the pH which is affected by makeup water or the addition of chlorine products. Sodium Carbonate or Soda Ash (Na2CO3) is used to raise the pH of pool water. It comes in powder form and is broadcast into the pool. Sodium Hydroxide or Caustic Soda (NaOH) is a highly corrosive liquid which is used to raise the pH, usually in pools with large volumes of water and when chlorine gas is used. It is pumped into the recirculating system at a controlled rate using a positive displacement type pump. Sodium Bicarbonate or Baking Soda (NaHCO3) is used to raise the total alkalinity and not appreciably change the pH. Total alkalinity greatly influences where the pH will stabilize to after a pH adjusting chemical is used. It is the measure to which a given amount of water is buffered. Total Alkalinity represents the amount of bicarbonate, carbonate and hydroxide alkalinity that is present. Their amounts depend on the pH of the pool. At the normal pH found in pool water most of the alkalinity is in the form of bicarbonate alkalinity. Total alkalinity should be maintained between 80 to 150 ppm in plaster pools and 125 to 175 ppm in non-plaster type pools. Hydrochloric Acid or Muriatic Acid (HCl), as well as Sodium Bisulfate or Dry Acid (NaHSO4), are used to lower the pH of pool water. No more than one-half quart of liquid acid per 10,000 gallons should be added at one time to a pool, otherwise damage to equipment can result. One hour should be allowed between half quart doses. Acid should be diluted in water and poured in the deep end of the pool and not into the skimmer or shallow end. When diluting acid, always pour the acid into the water not reverse. One should never refill an empty chemical container with a chemical other than the same chemical that originally came in the container. Excessive acid and low pH in pool water can lead to damaged equipment and cause bluish-green staining of the plaster when copper is leached from the recirculation piping and the heat exchanger. When pool water has been in an acidic state for an extended period of time, the water should be tested for copper. If level is over 0.2 ppm, the pool should be partially drained and refilled before adjusting the pH or else staining may result. Total hardness is a measure of the amount of calcium, magnesium and other metal ions in the water. When measuring hardness in pool water, one is measuring calcium hardness. The calcium hardness in pool water should be kept between 175 and 300 ppm. Too high a calcium level may lead to the formation of calcium carbonate or scale, with rough plaster surfaces, clogged piping, reduced circulation, heater in-efficiently, and eye irritation. Too low a level can result in etching and pitting of plaster, and corrosive water. If the calcium level is too high, the pool should be partially drained and refilled. If the level is too low, Calcium Chloride should be added. Low calcium hardness is usually not a problem on the west coast where make-up water is high in calcium hardness to begin with. Another indication of water quality is the level of Total Dissolved Solids (TDS) in the water. TDS is an electrochemical measurement of a waters ability to conduct an electrical current. TDS is a measurement only of charged particles in the water. Neutral particles are not measured in TDS. TDS is generally used to indicate when it is time to drain a pool. Make-up water coming into a pool may vary in its TDS level. Generally, a swimming pool should be drained when the TDS is greater than 2,000 ppm over its starting TDS, and for a spa when the TDS is greater than 1,200 ppm over its starting TDS. High TDS can lead to algae growth despite adequate chlorine residuals, interference of disinfectants in killing pathogens, cloudy water despite good filtration and chlorination, false readings on chlorine tests, and eye irritation. The Saturation or Langelier Index is a test that indicates if pool water has scaling or etching properties. The factors used to calculate saturation index are pH, water temperature, alkalinity, and calcium hardness. A saturation index of 0 indicates the water is balanced. A negative number greater than -0.5 indicates the water is etching and can be corrosive to metals in the pool and etch the pool plaster. A number greater than +0.5 indicates the water is scaling and can form calcium deposits which clog recirculation pipes and filter grids, and can stain pool plaster. In calculating the Saturation Index, factor values of water temperature, alkalinity, and calcium hardness are obtained from a Saturation index Table. These factors are added to the actual pH reading and the value of 12.1 is subtracted from the total. The result is the Saturation Index. ( Saturation Index = pH + temperature factor + calcium hardness factor + total alkalinity factor - 12.1 ). HOME - WHAT'S NEWS? - NOTICE BOARD -  BLUE PAGES - WIN PRIZES -  HOW TO... - RESEARCH CENTER-  CONTACT US © Copyright 2000 PoolTechs.com LLC All rights reserved. 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