Avoid Late-Season Pool Water Problems

August 25, 2023

The summer season is the time for communities to seek out the swimming pool. From Memorial Day until Labor Day, pools are filled with people splashing, swimming and playing, during which bather loads get heavy and outside temperatures rise.

Keeping pool water in near-perfect condition requires effort throughout the entire season, not just at openings and closings. Due to a variety of reasons, toward the latter half of the season, it is not uncommon to see water quality problems that have not presented themselves since the pool was opened. There are a few things pool operators and technicians should keep in mind to tailor recommendations to better prevent unsightly conditions before they become frustrating problems or hazardous to swimmer health. Remaining on top of pool maintenance routines will keep pool water clean until the very last days of summer vacation.

Keeping the Water Clean and Sanitized

Sanitizing the water of harmful organisms is one of the most important aspects of establishing an effective routine. Chlorine will kill most biological organisms present in the water, but there are numerous contaminants that can be removed without relying solely on chlorine. With increased demand for pool chemicals, there are other ways to help maintain the water as desired.

Since free chlorine has a short half-life under direct ultraviolet (UV) light and the chlorine residual depletes quickly, stabilizer in the form of cyanuric acid can be added for protection. Many trichlor-based tablets are formulated to further slow tablet dissolution. Some will have components with added benefits such as clarification or scale inhibition. A variable speed pump (VSP) is worth considering, in which the pool operators can program a schedule of different speed settings and run times throughout the day. There are also supplemental chemicals to help remove unwanted contaminants while chlorine targets biological organisms.

Oxidation importance
Rain, source water, swimmers, thunderstorms and nearby vegetation introduce waste products that need to be destroyed and removed. Some pool operators only apply oxidizers to remediate major issues, such as an algae outbreak or cloudy water. Shocking weekly to oxidize these contaminants introduced is typically a more economically sound way to help maintain a clean pool. During oxidation, electrons are transferred between hypochlorous acid and its target. Nitrogen and many nitrogenous compounds are a common target for chlorine because they react with chlorine readily. To prevent nitrogenous compounds from continuing to react with the free chlorine needed for proper sanitization, apply a maintenance shock weekly.

It is also effective to shock after rainstorms or heavy pool use. Physically removing visible debris such as leaves, pine straw or tree limbs as soon as they are apparent can help avoid major problems and chlorine depletion. Preventing contaminants from accumulating through use of a regular maintenance shock will help avoid fighting uphill and expensive battles with super-chlorination or water dilutions.

Water balance and impact on chlorine
Balanced water is not only important for protecting pool surfaces and equipment, but it also influences chlorine’s efficiency. When chlorine is administered to the water, it dissociates into hypochlorous acid (HOCl) and hypochlorite (OCl-). HOCl, the killing form needed to sanitize and oxidize, is most effective at sanitization when maintained in neutral environments with a pH range of 7.4 to 7.6.

HOCl ß à H+ + OCl-

Water with a lower pH shifts the equilibrium left to make more HOCl. If the pH exceeds 7.6, the equilibrium shifts to generate more OCl-, which is about 80 to 100 times less effective. Negatively charged microorganisms are repelled by OCl-’s weaker negative charge and, therefore, are not as effectively killed. Keeping the pH in mind is needed when selecting a chlorine form, whether it be trichlor, calcium hypochlorite, liquid chlorine or saline, as they all have differing impacts on the pH of the water.




















Influence of total alkalinity and sanitizer type
Keeping total alkalinity in range is also critical for controlling pH balance. A total alkalinity below 40 parts per million (ppm) causes pH swings that are difficult to correct. Low total alkalinity can decrease the pH, which can impact swimmer comfort and be detrimental to pool surfaces and equipment. Effects to alkalinity are important when evaluating the options for a chlorine-based sanitization program. Sodium hydroxide, the byproduct introduced by both salt chlorinators and sodium hypochlorite, drives a more alkaline environment where cloudy water or detrimental scale-inducing conditions if not counterbalanced by the appropriate amount of acid. At the opposite end of the spectrum, trichlor’s acidity over time erodes total alkalinity depending on quantity applied, and pH balance of source and rainwater. Total alkalinity should be measured weekly and maintained at 80 to 150 ppm to best maintain pH between 7.2 and 7.6.

Influence of water temperature on sanitizer and water balance
Water temperature is the single non-chemical balance factor to keep in mind, especially when extreme conditions occur. It is important in calculating the Langelier Saturation Index (LSI), and chlorine’s ability to control bacteria, algae and other microorganisms. Temperature, water hardness, total alkalinity, pH and total dissolved solids (TDS) are all a part of the calculation required to evaluate the overall water balance. Higher temperatures tip the water toward more scaling conditions, and lower temperatures create corrosive conditions. The warmer temperature from the first half of the season combined with high total alkalinity and high calcium hardness can force calcium out of solution and form scale deposits. Not only is scale unsightly and frustrating to remove, it can be problematic for pool equipment. For a chlorine generator, scale formation on the electrolytic cell can cause the generator to underperform and reduce its life expectancy. Cleaning the cell regularly with an acidic solution should help remove any hard deposits. A calcium sequestering agent should be added monthly to prevent this from happening, especially in pools with higher-than-average total alkalinities.

Warmer water has a great impact on chlorine as well. Chlorine degrades faster in warmer conditions, especially if adequate stabilizer is not present to block out UV from sunlight. During June and July, the water temperature is at its warmest, often exceeding the normal 78-to-82 F range in some places (such as Texas has been experiencing recently). The warmer water speeds up dissolution of slow-dissolving tablets, which may require more frequent replacements if the free chlorine residual is not being maintained. The warmer temperature and the wet environment make a comfortable place for organisms to thrive, which means free chlorine has more work to do. Testing measurable free chlorine regularly is imperative. Testing will reveal more chlorine is needed, especially as more swimmers take advantage of the warmer water. A booster shock may be needed to break up combined chlorine, or the output of a chlorinator may need an adjustment. Understanding the pool’s behavior, events and the surrounding environment as the summer moves along is important to making the appropriate changes to the routine.

The warm and wet environment is particularly appealing to algae. Being sure to brush stagnant areas, at least weekly, will be necessary. Adding a maintenance algaecide weekly, as opposed to biweekly, should be explored. Quat-based algaecides will tackle most types, but if the pool is in an area where more resistant types are common, a polyquat or a chelated copper-based algaecide would be better choices. How much and how often free chlorine needs to be replenished varies depending on water circulation and filtration patterns, bather load, source water and even the natural surrounding environment.

Colder water and LSI
Most residential pools operate between 78 and 82 F during the pool season, but warmer water is not the only temperature extreme to keep in mind. Cooler temperatures make the water more corrosive to a pool’s equipment, especially the heater. Prolonged exposure to surfaces may cause etching. Metal staining may be more prominent as well. A metal chelating product or sequestrant should be included in the routine, especially when pool temperatures drop toward the end of the season or for those with unheated pools. Filter aids, following the use of a chelating product, such as a charged cellulose can be used to help better guide problem-causing metals to the filter, where they can be eventually permanently removed. Temperature does vary, especially in more northern regions where water may not reach average temperatures without a heater. Remember, the water could be in range for pH and total alkalinity but still lean on the corrosive side with colder temperatures. This will also be important for best winterization practices at the end of the season.

Ancillary products—clarifiers and enzymes
Sanitization is highly important to keeping the pool clean, but it should not be the only component. Ancillary chemicals, such as clarifiers or enzymes, can help break down non-living contaminants so chlorine does not have to waste its energy in their removal. Clarifiers can help bind small particles together into bigger polymeric chains the filter will be able to hold onto. Chlorine and adequate filtration will remove visible contaminants from the water, but oils and dirt inevitably deposit along the waterline despite standard efforts. An enzyme is a naturally derived catalytic protein that can often be used to break down organic matter into more manageable forms. Specialized enzymes are often picked for removing nitrogenous amino acids, fats or oils. Some products even pair different types of enzymes together to combat more than one type of contaminant. Many products will incorporate enzyme technology with a surfactant or phosphate remover. The synergistic relationship of enzyme and surfactants make dual-action ancillary maintenance product performance results more improved. With surfactants, a hydrophobic “tail” attaches to oils at the surface, while a hydrophilic “head” lifts oils from the surface where they enter the water to be broken down and removed by filtration. These also help prevent oily buildup in the filter. Phosphate-removing products can help prevent calcium phosphate precipitation, and even have clarifying abilities of their own. The elimination of these oxidizable non-living wastes reduces the demand on chlorine and improves the overall water quality.

Every pool has its own unique behaviors and nuances. Using a smart maintenance plan and being flexible to adjust as necessary will help overcome the late-season slumps pool owners often face. In addition to remaining on top of the free chlorine residual, using supplemental products will all work together to keep a pool a fun, clean and relaxing place for everyone in the community to enjoy until the summer ends.

About the Author
Emily Johnson, born and raised in South Carolina, graduated with a bachelor of science degree in biological sciences and minor in chemistry from the University of South Carolina. She is a recreational water enthusiast living in Atlanta, Ga., with her two rescue dogs who love a good dip in a splasher pool. She has been working for research and development at BioLab Inc., a KIK Consumer Products Company, since 2014. For more information, visit www.biolabinc.com.