The Important of Pool and Spa Water Testing

The Significance of Pool and Spa Water Testing

     Residual Disinfection and pH Control

          In terms of swimming pool treatment, disinfection or sanitizing basically means to rid the pool of bather pollution, destroy bacteria, and control nuisance organisms like algae, which may occur in the pool, filtration equipment and piping. There are a number of techniques used, namely, chlorine, bromine and ozone dosing systems, of which chlorine is the most common.

Chlorine

         Chlorine is a strong oxidizing agent that destroys organic pollutants and bacteria. Chlorine combines with compounds containing nitrogen to form chloramines, during which only part of the chlorine will be used while the rest remains active, continuing it’s disinfecting action.

         Combined chlorine is the quatity of chlorine that has already combined with nitrogen containing compounds, it is much less effective as a disinfectant than free chlorine, which has yet to make the transition. The addition of combined chlorine, and free chlorine gives total chlorine. A pool manager needs to aim for the perfect balance where free and total chlorine are proportionally equal, and thus to keep the combined chlorine level near zero. The presence of chloramines is undesirable because of the distinctive “swimming pool smell” as well as irritation to the eyes and mucous membranes caused by combined chlorines like dischloramines.

             Commercial chlorine for disinfection may be available as a gas(Cl₂), a liquid like sodium hypochlorite or bleach(NaOCl) or in a solid state like calcium hypochlorite, Chlorohydantoins or chlorocyanuric acid compounds. These compounds, once dissolved in water, establish equilibrium between the hypochlorous acid(HOCl) and the hypochlorite ions(OCl^-). Although both forms and considered free chlorine, it is the hypochlorous acid that provides the strongest disinfecting and oxidizing characteristic of chlorine solutions. The amount of hypochlorous acid in chlorinated water depends upon the pH value of the solution, Changes in pH value will effect the HOCl equilibrium in relation to the hydrogen and hypochlorite ions.

            As depicted by the graph, HOCl decrease and OCl^- increases as pH increase. At a low pH, almost all the free chlorine is in the molecular form HOCl, and atpH of around seven point five, the ratio between HOCl and OCl^- is 50 : 50. Since the ionic form OCl^- is a slow acting sanitizer while the molecular HOCl is a fast acting, it is important to measure pH regularly. As a general rule a pH of about seven point two is recommended to maintain fast acting disinfection conditions.

Bromine

    In many countries bromine sanitizing has been introduced as an alternative for chlorine, although it is not as strong. The advantage of bromine lies in its stability at higher temperatures(advantageous for heated pools and hot tubs), and its maintained disinfection power at a higher pH. Futhermore, there is very little reaction between bromine and nitrogen compounds, reducing the unpleasant odor, and eye irritation problems. The main disadvantage of bromine is the slower acting disinfecting power, making it less suitable for larger pools.

Ozone

                  Ozone is a very strong oxidizing agent that destroys organic compounds that are especially difficult to oxidize. It allows the pool manager to very efficiently remove combined chlorine without frequently refreshing large amounts of pool water. By the time the water passes through the filter units, ozone has already completed sanitizing and it is not effected by the pH level.

             Mainly because of its strong oxidizing power, the return water may contain trace concentrations of ozone. It imperative to know that ozone is very unstable, so to ensure thorough sanitization of the water, low – level chlorination remains necessary.

The water Balance and Langelier Index

        Pool water Characteristics need to be maintained in a balanced state to avoid numerous issues. Measuring certain variables is extremely important to predict of the water is corrosive, scalling or balanced. A saturation index developed by Dr. Willfred Langelier is widely used to predict the balance of swimming pool waters. It represents the estimation of a solutions ability to dissolve or precipitate calcium carbonate deposits. A certain level of this precipitation(filming) is desired to insulate pipes and boilers from contact with water. When no protective filming is formed, water is considered to be corrosive. On the other hand, too much filming can develop into scaling and incrustation of the pipes.

          In the treatment and monitoring of pool water, the pool manager must ensure that related parameters such as alkalinity, hardness and pH and dutily taken into consideration.

The Langelier Index is a powerful tool to calculate the water 
balance, and to predict corrosion or scaling problems. Theoretically, a LI of zero indicates perfect water condition for swimming pools. If LI > 0, scaling and staining of the water is present, and if LI < 0 the water is corrosive and highly irritating, A tolerance of +/- 0.4 is normally acceptable.

     The Langelier formula is expressed as :
LI = pH + TF + HF + AF - 12.5
Where : 
LI = Langelier Index(also called Saturation Index)
pH = pH of the water
TF = temperature factor.
HF = hardness factor, log(Ca hardness, ppm as calcium carbonate)
AF = alkalinity factor, log(alkalinity, ppm as calcium carbonate)

     To calculate the exact Langelier Index of your water please use the water Index reference tables.
      For most pools, water is balanced if :
** The pH value is maintained within the recommended ranges of pH 7.2 - 7.6
** Ideally the Alkalinity should be maintained within a range of 80 - 125 ppm.
** The Calcium Hardness should be maintained within a range of 200 - 400 ppm.

         To calculate your water balance, three parameters must be measured, calcium hardness, alkalinity and pH. Find the hardness and alkalinity factor in the Water Index reference tables below. The water temperature is, in general, maintained between 24 degree celcius and 34 degree celcius. Assuming the temperature is kept within those ranges, an average value or 0.7 may be used.

        Water Balance = pH+TF+HF+AF

 Calcium

          The presence of calcium in the system is desired to ensure filming on those places where the temperature is relatively high, like in boilers and pipes transporting warm water. Scaling must be avoided because it reduces heat transfer and pump capacity, and causes cloudiness in the water. It is recommended to maintain the calcium hardness value within the range from two hundred to four hundred as calcium carbonate(CaCO₃).

Alkalinity

          Alkalinity is the measure of the total concentration of alkaline substances, mostly bicarbonates, dissolved in the water. The higher the alkalinity, the more resistant the water is to pH change. At the same time, high alkaline water is a major contributor to scaling problems like incrustation in filtration equipment, pumps, and piping.

pH

     It  is recommended to maintain the alkalinity value within the range from eighty to one hundred and twenty-five part per million as calcium carbonate(CaCO₃)

    The pH of the water is an important factor since at lower pH levels the corrosion rate increase. If the alkalinity values are sufficiently high, it will not be difficult to control the pH. Most pool managers prefer to keep the pH between seven point two and seven point four to best maintain low corrosion rates and a sufficient activity of chlorine.

   Around the world, swimming pool and spa facilities welcome dozens, even hundreds of people on a daily basis. A basic necessity of pool water treatment is to maintain the water in a safe and plesant condition for the bathers. In order to achieve ideal water conditions, swimming pool water requires testing on a daily and sometimes hourly basis for disinfection of residuals and maintaining pH levels. Equally important, calcium hardness and alkalinity levels should be monitored weekly to ensure the pool water is well balanced, thus to avoid corrosion and scale formation.