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.