The importance of indoor swimming pool maintenance
Swimming pools must be well designed, maintained and operated to prevent the spread of disease and be comfortable for swimming. Pools need disinfection to destroy micro-organisms and filtration to remove pollutants. Effective ventilation is also essential to remove any air impurities and reduce condensation.
Indoor swimming pools and chloramines
Chlorine is the most common form of swimming pool disinfection. When chlorine is added to water free chlorine is formed. Free chlorine is the active disinfectant chemical form of chlorine. Chloramines, also known as combined chlorine, are formed when free chlorine reacts with ammonia like compounds called amines.
Free chlorine + ammonia compounds = nuisance chloramines (combined chlorines)
"Free Chlorine" is measured by the use of DPD#1 tablets . "Total Chlorine" is measured when DPD#3 tablet is the added and the colour deepens after a few minutes. The difference between "free chlorine" and "total chlorine" is "combined chlorine" otherwise know as "chloramines".
Amines are introduced into the pool mainly by urine and perspiration. Chloramines are poor disinfectants and greatly reduce the disinfection power of free chlorine, irritate mucous membranes, cause eye stinging and red eyes, and irritate respiratory systems. The strong chlorine odour often smelled at poorly operated pools is caused by chloramines not free chlorine.
To limit the formation of chloramines pool operators should limit the amount of ammonia entering the pool by encouraging swimmers to use the toilet and to shower with soap before entering the pool. This is particularly important for infants who are not toilet trained and incontinent people.
Chloramines must be "burnt out" or oxidised by adding more oxidiser such as chlorine. Another way to prevent a build up of chloramines is to ensure that there is a large excess of free chlorine to combined chlorine to constantly burn out chloramines.
Legally combined chlorine (chloramine) must not exceed 1mg/L in any public swimming pool and spa pool, and pool operators should ensure as best practice that combined chlorine never exceeds half of the concentration of free chlorine.
Controlling chloramine problems
Continuous breakpoint chlorination
Continuous or daily breakpoint chlorination is a technique which burns out chloramines over-night so that breakpoint is reached by morning. Continuous breakpoint chlorination is best practice in swimming pool operation. There is a separate fact sheet which thoroughly explains the continuous breakpoint process.
Shock superchlorination (shock breakpoint chlorination)
Shock superchlorination is a technique used to control a severe excess of chloramines. However, if it is not performed correctly it can result in even more problems for the pool operator. Superchlorination must be carried out after the pool is closed to swimmers for that day. Maximum ventilation must be provided to remove all chloramines that form and volatilise into the air. Regular fortnightly superchlorination may be necessary dependent upon the amount of ammonia into the pool and whether continuous breakpoint chlorination is practised.
Shock superchlorination is practiced by adjusting the pH to 7.5 or lower and by the addition of sufficient chlorine to achieve a free chlorine concentration ten times the combined chlorine concentration. The pool circulation and filtration systems must be operated over-night. By morning the chloramines are oxidised and when all of the total chlorine is free chlorine then breakpoint is reached. A pool consultant should be engaged initially to ensure that shock superchlorination is carried out in a safe and efficient manner.
Shock dosing with oxygen shock products
Hydrogen peroxide and potassium mono-persulphate are two common oxygen shock products that can be used to control chloramines in heavily used pools. These products lower the chlorine demand by oxidising pool contaminants thereby allowing free chlorine to better perform its disinfection role. Their use may lead to false high total chlorine measurement in the pool water for about one to two days after addition.
Ultra violet light systems
Medium pressure lamp ultra violet (UV) light systems reduce chloramine concentrations significantly. Recent evidence suggests that UV light systems, besides providing additional disinfection, also inactivates chlorine resistant micro-organisms such as the parasitic protozoans Cryptosporidium parvum and Giardia lamblia. Because UV light does not impart a residual disinfectant to the pool water chlorine must still be used at recommended concentrations.
Ozone may be used to control chloramines and has good disinfection properties. Ozone may be used in addition to, but not instead of, chlorination. Pools utilising ozone must quench the ozone using a granular activated carbon filter before the water is returned to the pool. The exception is the use of low dose ozone (up to 2g/hour) where the ozone is pumped with air through a venturi into a mixing chamber and reaction vessel in the circulation system after the pool water has been filtered. Provided the ozone is thoroughly mixed and dissolved, it reacts rapidly to destroy chloramines and disinfection by-products to reduce tastes, odours and eye stinging compounds.
Dilution with fresh water
Town mains water can be used to dilute chloramines and will also reduce total dissolved solids (TDS). However, incoming mains supply water may contain monochloramine and should be tested to determine its concentration. The presence of high concentrations of monochloramine may not reduce chloramines in the pool. The use of water from rainwater tanks to top-up swimming pools is recommended, provided first flush systems and other controls are in place to protect public health. Rainwater does not contain chloramines and is very low in TDS.
Ventilation is essential for efficient removal of chloramines and other air impurities. Chloramines when given off from a pool in the form of a gas will redissolve in the pool unless removed by an efficient ventilation system. A ventilation system needs to be well designed without causing drafts, to expel stale air, induce fresh air and lower humidity. The use of pool blankets at night prevent chloramines from escaping and they may reform in the pool.
The Public Swimming Pool and Spa Pool Advisory Document provides detailed explanations and information on disinfection, pool chemistry, risk assessment and other issues relevant to swimming pool operation.
Public swimming pool issues may be discussed with an environmental health officer at a local Public Health Unit: or your local council.
In NSW call 1300 066 055 to talk to your local Public Health Unit.