When considering factors affecting chlorine consumption, several aspects come to mind, primarily revolving around water temperature and pool usage patterns. As the water temperature increases, there is a tendency for accelerated organic growth, which in turn heightens the demand for chlorine. Even in the presence of CYA, the sun’s exposure can exert a chlorine-drawing effect on the water. Further, the frequency of pool usage plays a significant role in chlorine consumption, with more frequent use translating to higher chlorine use.
Another crucial aspect to explore pertains to the pool’s surroundings and the property itself. For instance, a pool situated in a desert region might contend with dust and dirt carried into the pool by the wind, but this is typically not a major contributor to chlorine demand. However, individuals with intricate landscaping or trees that shed particles may experience excessive chlorine demands. Particularly when winds pick up, pollen, nectar, and other organic matter from vegetation can find their way into the pool, further depleting the chlorine reserves.
Assessing the combined factors of pool use and external environmental conditions is essential for making well-informed decisions regarding the course of action to take when CYA levels exceed 100 ppm. For instance, if the pool is situated in a spacious, sheltered location that is not prone to external influences such as heavy rainfall and experiences infrequent use, it may be possible to maintain CYA levels above 100 ppm with minimal adjustments to the daily maintenance routine.
Safety should always be a top priority when it comes to pool water. It is important to keep in mind that even with elevated CYA levels, chlorine continues to function as an oxidizer. As long as a free chlorine residual of at least one ppm can be upheld, CYA does not significantly impede the ability of OCl- or HOCl to deactivate or eliminate common germs and bacteria. While the rate of sanitation and inactivation may decrease, the presence of free chlorine still holds the potential to contribute to the safety of the water.4
Regrettably, the increased presence of CYA does indeed diminish chlorine’s capacity for oxidation. Upon the introduction of CYA into the water, the millivolt (mV) levels immediately commence a decline, thereby reducing chlorine’s effectiveness in disinfecting the pool.5 For example, when the CYA concentration reaches 75 ppm, it can decrease the oxidation reduction potential (ORP) to approximately 185 mV.6 The minimum acceptable ORP reading should not fall below 600 mV,8 with an ideal target being around 750 mV. At these ranges (600-750 mV), and assuming the pump and filtration system are operating at peak efficiency, water quality has the potential to be at its best. More importantly, water will be at its safest for bathers, assuming there has not been a more
heinous incident like a fecal release or other biohazard contamination.
Fortunately, if CYA levels continue to rise, particularly surpassing the 100-ppm threshold, the rate at which ORP declines tends to stabilize. However, since elevated CYA presence hampers the removal of germs and bacteria, it becomes necessary to add more chlorine (or another oxidizer) at more frequent intervals to mitigate waste buildup and prevent common water-related issues.
In the presence of heightened CYA levels, several strategies can be employed to maintain clean and clear water. One approach involves elevating the chlorine level, where maintaining a free chlorine level at 7.5 per cent of the total CYA concentration is a commonly practiced method. Another option is the use of alternative oxidizers, such as potassium monopersulfate, to combat water contamination. These alternative oxidizers do not form bonds with CYA like HOCl, thus preventing a decrease in ORP. In fact, shortly after using potassium monopersulfate, ORP levels will spike ORP reading until the oxidizer has run its course, which can be fairly quick (minutes to hours) if there are sufficient organic contaminants.
