pH
pH is a measure of the water’s hydrogen ion concentration. It is the most important non-disinfectant balance parameter, as it has a significant impact on water balance and a direct correlation with turbidity. It is also the component around which all other parameters are balanced.
Water is considered to be the ‘universal solvent,’ which means it will dissolve nearly any inorganic material until it reaches a point where it is satisfied. Satisfaction for a certain material is termed solubility, which has an inverse relationship with pH. This means water at a lower pH will have a greater capacity to dissolve minerals before satisfaction.
The impact on cloudiness lies in changes in pH, rather than the particular pH value at any given time. For instance, if water reaches equilibrium at a certain pH, e.g. 7.2, but then rises to 8.0, the water will become oversaturated with dissolved minerals. The excess minerals will then become insoluble and precipitate out of the water as metal salts or metal oxides.
Referencing the calcium carbonate equilibrium equation, a rise in pH will drive the reaction toward the precipitation of calcium carbonate scale. Once precipitated, the scale exists as small, suspended particulate matter (PM), which gives the pool water its cloudy appearance. The only way to remove the particulate is re-dissolution through reduction of pH or by physical removal via filtration.
Total alkalinity (TA) and calcium hardness
Total alkalinity and calcium hardness also play a factor in water balance and contribute to water turbidity. They are primary components that help buffer pH and maintain a mineral level that is sufficient in keeping the water satisfied and in a condition where it will not corrode other equipment components.
Due to the fact calcium and alkalinity (AT) are maintained at such high concentrations relative to any other component in the water, calcium carbonate is the predominant equilibrium relationship in pool systems. Based on the equilibrium equation, the reaction is dependent upon concentration of calcium and carbonate ion (CO2-3) in the water. An increase in either component drives the reaction toward scale formation, much like a rise in pH. Insoluble calcium carbonate scale is formed, creating water turbidity.
Temperature
The third factor that significantly impacts calcium carbonate equilibrium is the water’s temperature. Unlike many other solutes, calcium is inversely soluble with water temperature. Due to the carbon dioxide (CO2) equilibrium component, this means the solubility of calcium decreases as the water temperature increases. The reason for this is warmer water volatilizes more carbon dioxide by gassing it off to the surrounding atmosphere, resulting in the formation of calcium carbonate scale.
Disinfectant concentration
Although the concentration of hypochlorous acid (HClO) in the water has no impact on calcium carbonate equilibrium, a deficiency can impact water turbidity.
Suspended solids do not have to be inorganic, they can also be biological. For instance, algae growth can significantly impact the cloudiness of water. If the pool water is in a chlorine demand situation, then algal or microbial growth is supported. Once these organisms colonize, they spread throughout the water causing it to appear hazy.
If algae growth is supported for too long, the water takes on a green, swampy appearance, resulting in reduced visibility and large sanitizer demands. In these situations, the only way to reduce turbidity is to add enough sanitizer to break the demand and inactivate the micro-organisms. The dead algae and organisms must then be physically removed from the water through filtration or flocculation.
Physical causes of cloudy water
Although improper chemical balance contributes to cloudy pool water, inadequate filtration is a more significant cause. Many different variables can impact the filtration system’s effectiveness; however, the consequences of each can be mitigated through proper maintenance procedures, which begin with adequate pump operation.
