Practical approaches to cyanuric acid reduction in chlorine

by arslan_ahmed | October 25, 2023 6:00 am

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By Kevin Vlietstra

Chlorine is a vital component for maintaining the safety of pool water for swimmers. Its primary function is to serve as a sanitizer, but it also has the added capability of acting as the primary oxidizer of waste and preventing the proliferation of algae. When there is an abundance of chlorine available, it can efficiently perform all three of these functions. However, in situations where chlorine is in short supply, it becomes necessary to introduce supplementary substances. These supplements can serve to either reduce the overall quantity of chlorine required or extend the lifespan of the existing chlorine within the water.

One common additive used for this purpose is cyanuric acid (CYA). It is frequently used to stabilize, safeguard, and conserve chlorine, regardless of whether it is in tablet or liquid form. This article will primarily focus on CYA’s role in preserving chlorine and delve into its impact on water quality as it accumulates in the pool.

Understanding the role of CYA

In discussions concerning chlorine and cyanuric acid (CYA), it is essential to provide an overview of the two categories of chlorine used for water treatment: chlorine with stabilizers and chlorine without stabilizers. Chlorine types lacking stabilizers encompass sodium hypochlorite (commonly known as liquid chlorine bleach) and calcium hypochlorite (often abbreviated as cal-hypo). On the other hand, chlorine varieties with stabilizers are typically referred to as “trichloro” or “dichlor.” These product names reflect their respective manufacturing processes. For instance, trichloroisocyanuric acid (trichlor) is produced by reacting certain ingredients with CYA to generate a concentrated granular chlorine.

Upon the application of dichlor or trichlor to fresh water, CYA becomes introduced into the pool environment. The stabilized chlorine also yields hypochlorous acid (HOCl), which binds with the CYA. Consequently, HOCl retains its effectiveness for a longer duration when the pool is exposed to outdoor conditions and ultraviolet (UV) light. Initially, even at just one part per million (ppm) of CYA, chlorine remains in the water for an extended period compared to its absence. As the CYA concentration reaches approximately 25 ppm, a more significant amount of chlorine (HOCl) is shielded from degradation in the presence of UV light.¹ This not only prolongs the presence of chlorine in the water but also translates into time and cost savings for pool owners.

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Using chlorine compounds with stabilizers results in a continuous introduction of CYA into the pool water. Nevertheless, once CYA concentrations reach 50 ppm, the advantages of chlorine retention begin to plateau. When considering even higher levels, such as 100 ppm, there are no substantial benefits associated with further increasing the CYA content in the water.²

Upon closer examination, when chlorine is introduced into the pool, it leads to the formation of hypochlorite ions (OCl-) and HOCl. The latter serves as the potent disinfectant produced when chlorine interacts with water. On the other hand, OCl- also possesses disinfection capabilities but to a significantly lesser extent.

When the pH level is maintained at 7.5, there is an equilibrium established, with an equal ratio of HOCl to OCl-.³ However, as the pH rises above 7.5, there is a reduced concentration of hydrogen ions, resulting in a greater formation of OCl-. Conversely, when the pH drops below 7.5, more hydrogen ions are present, leading to an increased presence of HOCl.

Ideally, one would aim to operate a pool with a lower pH to favour the production of more HOCl, which is highly effective in disinfection. Nevertheless, it is essential to consider the potential corrosive effects on various pool components that come into contact with the water. Striking a balance around 7.2 is often recommended, as it allows for effective chlorine action while minimizing the risk of pool corrosion.

That said, another influential factor affecting the availability of HOCl is the presence of CYA. When even a small amount of CYA is introduced into chlorinated water, it immediately exerts a detrimental effect on the dissociation of HOCl and OCl-. As more CYA is added to the pool, this impact is compounded, resulting in a substantial reduction in the quantity of HOCl present.

While the presence of CYA typically maintains a level of HOCl that is generally effective for residential pools, its impact becomes considerably more significant in commercial pools. This becomes especially critical in water environments that may accommodate multiple simultaneous users, as it can significantly hinder water disinfection rates. To put it more plainly, as it pertains to commercial pools, cyanuric acid should not be used to help ensure the safest possible water for users.

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The decision on CYA levels

Manufacturers and standards organizations have established a reference level of 100 ppm as the threshold for excessive CYA in pool water. This guideline serves as a practical benchmark, ensuring consistency in information among service personnel and providing a baseline for pools that have experienced past issues related to water quality or algae growth. Nevertheless, the ultimate decision regarding the maintenance of higher CYA levels rests with the pool owner.

In assessing the severity of elevated CYA levels in a specific pool, it is crucial for the pool service professional to engage in a discussion with the owner. Together, they can determine whether immediate action or future measures are necessary. The primary concern revolves around the conditions that may lead to chlorine consumption within the water.

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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.

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Additionally, water treatment can involve the use of non-oxidizer additives. Enzymes, for instance, prove highly effective as they aid in breaking down complex molecular structures that might otherwise hinder chlorine’s effectiveness. When a cell structure is unravelled or deteriorated, this allows an oxidizer to easily reduce it from the water. Borate products can contribute to increased water clarity, though its bonding with calcium and other substrates. Additionally, borates can contribute to the stability of water balance by introducing a secondary buffering agent to the water. Further, maintaining low phosphate levels can provide relief in situations of reduced chlorine levels. Regularly cleaning filters to remove grease and oily deposits with dedicated solutions can also reduce the reliance on chlorine. Finally, the use of algaecides can be beneficial in diminishing the presence of algae.

What are the options for decreasing CYA levels?

Reducing CYA levels can be a challenge, as there are not many reliable methods available. While chemical treatments do exist, often enzyme based, following the precise instructions can be demanding for the person applying them. Another option involves using a portable reverse osmosis system (RO). These systems, at least currently, are large and usually expensive which are typically wheeled into place. When auxiliary hoses are placed into the water, RO uses high pressure to force water through a membrane which reduces everything in the water from calcium to cyanuric acids.

Cyanuric Acid (CYA) Testing

1. Sample collection. While obtaining a sample from a return may yield uncertain outcomes for pH and chlorine levels, it can offer a more precise measurement for cyanuric acid (CYA),particularly when water is drawn from both the bottom and the surface. When conducting an initial test following a period of water stagnation during the entire off-season, it is advisable to brush all surfaces and allow the water to circulate for 24 hours before obtaining the first sample. 2. Testing. There are three main methods for testing CYA. a. Test strips can help provide a general idea of CYA levels. b. A visual examination which involves introducing melamine or a comparable agent into the water. The mixture is then added to a chamber until a visual indicator disappears. This is fairly accurate, but some interpretation may be needed when reading the results. c. Photometers take the guesswork out of test results. As long as the machine is calibrated correctly and filled according to the manufacturer’s directions, the results should be fairly accurate.

It is crucial to note that a significant portion, potentially up to 25 per cent, of the total CYA can settle in areas of the pool with poor circulation. Therefore, removing water from the lowest part of the pool becomes essential in diluting the water and reducing CYA levels. Recent recommendations within the industry say the use of aluminum sulfate (alum) may aid in CYA reduction.⁹ However, more studies are needed as there are no outside scientific papers to help draw a line between aluminum sulfate and CYA reduction. Regardless of the method chosen for water removal, it is important to replace water with elevated CYA levels with fresh water, specifically water with no cyanuric acid, to effectively address the issue.

It is worth considering most of the comments and recommendations provided here are focused on residential pool care. However, it is important to emphasize that cyanuric acid in water has not been linked to any documented cases of water-related illnesses. Unsafe water conditions typically arise from factors such as inadequate chlorine levels, poor water balance, and other subpar water care practices. Those factors will lead to issues like the proliferation of bacteria and virus and the growth of unwanted organics and other contaminants. These specifically point to algae and slimes, which have their own issues, can also lead to accidents caused by slippery pool bottoms. Managing elevated CYA levels is an integral part of swimming pool care, contributing
to the overall ease of water treatment
and maintenance.

Notes

¹ See “Cyanuric Acid: Revised—September 2011” published by the Pool & Hot Tub Alliance (PHTA). For more information, visit www.phta.org/pub/?id=0838089D-1866-DAAC-99FB-D64EE07EA13F[6].

² See note 1.

³ See “The Fundamentals of Chlorine Chemistry and Disinfection”, December 2007. For more information visit: https://dnr.wi.gov/topic/labcert/documents/training/CL2Chemistry.pdf[7].

⁴ See “Cyanuric Acid: CMAHC Ad Hoc Committee Report” published by the Council for the Model Aquatic Health Code (CMAHC) on Oct. 18, 2017. For more information, visit https://cmahc.org/documents/CMAHC_Ad_Hoc_Committee_Report_on_Stabilizer_Use._WAHC_2017-10-16_FINAL.pdf[8].

⁵ See “Oxidation-reduction potential” published by the New South Wales Government on Nov. 14, 2016. For more information, visit www.health.nsw.gov.au/environment/factsheets/Pages.orp.aspx.

⁶ See “Frequently Asked Questions about OxyChem’s ACL Chlorinated Isocyanurates” published by Occidental Chemical Corporation. For more information, visit www.oxy.com/globalassets/documents/chemicals/products/other-essentials/acl_faqs.pdf[9].

⁸ See “Minimum ORP Reading”, Model Aquatic Health Code, 4^th Edition, 2023: https://cmahc.org/mahc_sections/776[10].

⁹ See “Aluminum sulfate for cyanuric acid removal” published by Service Industry News on Oct. 31, 2020. For more information, visit www.serviceindustrynews.net/2020/10/31/aluminum-sulfate-for-cyanuric-acid-removal[11].

Author

Kevin Vlietstra is the technical director and regulatory specialist with Haviland Pool and Spa Products. He has been working in the recreational water industry for more than 25 years. Vlietstra can be reached via email at kevinv@havilandusa.com.

Source URL: https://www.poolspamarketing.com/trade/features/practical-approaches-to-cyanuric-acid-reduction-in-chlorine/

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