Turbidity is one of the most predominant water quality issues in the pool industry. Fortunately, pool owners can recognize cloudy water and know it’s an indication that something requires attention. However, the difficulty then becomes diagnosing the problem and providing a solution.
The cloudiness or haziness of water is caused by introduction of suspended particles that are invisible to the naked eye. These impurities are introduced from a variety of sources including particulate debris from the air, dirt, pollen, algae, or microbial organisms. Even bathers and source water contribute to the impurities that cause cloudy water.
When we discuss the causes of turbidity in pools, we are specifically referring to the failures of proper management that allow for particulate accumulation. Pool systems prevent cloudy water according to two distinct mechanisms: chemically through proper water balance and physically through filtration.
Improper water balance is the most significant chemical cause of cloudy water. The following sections discuss each parameter and their respective impacts on cloudy water.
pH is the cornerstone around which all other components are balanced and because of this, it has a direct correlation with turbidity. Water at a lower pH will have a greater capacity to dissolve minerals. The impact on cloudiness lies in changes in pH. For instance, if water reaches equilibrium at a pH of 7.2 but then rises to a pH of 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, metal oxides or calcium-based compounds which can adhere to surfaces and form scale. The only way to remove these particulates is re-dissolution through reduction of pH or removal through filtration.
Total alkalinity and calcium hardness
Total alkalinity and calcium hardness are other components necessary to water balance that can contribute to water turbidity. They help buffer pH and maintain a mineral level sufficient to keep the water satisfied. If either total alkalinity or calcium is too high, then the calcium compounds will become insoluble, creating water turbidity and potentially scale on pool surfaces.
The third factor that significantly impacts calcium carbonate equilibrium is water temperature. Unlike many other minerals, the solubility of calcium in water decreases with rising temperature. The reason for this is the carbon dioxide equilibrium that exists in water. Warmer water volatilizes more carbon dioxide, gassing it off to the surrounding air. The reduction of carbon dioxide can contribute to the formation of calcium carbonate scale.
Though the concentration of sanitizer in the water has no impact on water balance, a deficiency can impact water turbidity. Suspended solids can also be biological. For instance, algae growth can significantly impact the cloudiness of the water. If the pool is in a chlorine demand situation, then algal or microbial growth is supported. In this scenario, the only way to reduce turbidity is to apply enough sanitizer to break the demand and inactivate the microorganisms.
Inadequate filtration is the most significant cause of cloudy water. Several variables can impact the effectiveness of the filtration system.
Pump run time
Pump run time is the amount of time that a pool’s circulation system runs each day. Inadequate pump run times will not apply enough filtration to the pool to remove the contaminants that contribute to cloudy water.
Dirty filter media
Another physical cause of cloudy water can be dirty filter media. As the media removes particles, the void space in it becomes full. This leads to smaller particles being removed as the diameter of the void channels decreases. This places additional resistance to the system, increasing operating pressure and decreasing flow rate. This causes an increase in turnover rate which means fewer turnovers in a given time frame. Fewer turnovers can often lead to cloudier water. Proper filter maintenance must be performed to ensure adequate filtration. As a general rule of thumb, filters should be backwashed or rinsed (according to media) when the filter pressure is 10 psi higher than normal operating pressure.
Other physical causes
Aside from being dirty, the life of the media can negatively impact filtration performance to yield cloudy water. For instance, the surface of a sand grain is very rigid, with nooks that act as attachment sites. This aids in filtration as it increases the surface area available to remove microscopic particles from the water. Over time, the sand tends to smooth out. As such, the surface area for filtration decreases and performance is affected. Cartridges can also deteriorate over time. Therefore, these media should be replaced periodically.
Channeling of sand filter beds is another issue that can hurt filtration. The water flows faster at certain points than others, causing a channel to develop through the media bed. These channels become the modes of water transport through the filter. Once established, filtration is significantly diminished, as water flowing through the channels circulates through the system unfiltered. The only way to correct a channeling issue is to replace and regenerate the filter bed. In addition, a tear in the fabric of a filter cartridge or a broken DE grid will provide a channel of water to flow through without being filtered.
In many cases, the application of a filter aid will help clear cloudy water much faster. Flocculents and clarifiers make smaller particles larger. The larger particles can fall to the bottom of the pool to be vacuumed or trapped by the filter.
If we as pool professionals understand that a cloudy pool is a symptom of a problem, rather than the disease, we can ask targeted questions that lead us to the right solutions. The ability to provide those solutions to our customers illustrates our value as professionals, driving customer loyalty and sustainable profitability.