Cyanuric acid seems to be taking a bit of a hit lately.

It’s been decades since the chlorine stabilizer hit the market and changed service forever. Before, chlorine required multiple replenishments throughout the week. With cyanuric acid (CYA) in the picture, chlorine was protected from sunlight deterioration and could last in the water for days. Now weekly service visits sufficed, and techs could take on more accounts. And the pressure was off DIYers, who could spend less time caring for their pools.

But no substance is perfect, and CYA brings with it some concerns. Current, experts are looking at how the very phenomenon that enables CYA to do its job — its molecular bonding with chlorine, which protects it from the sun — also means that a certain amount of the sanitizer lay dormant at any given moment. On the residential side, some experts have researched the matter and now believe that excessive CYA use contributes to algae formation if not enough chlorine is available. In the commercial realm, regulators and standards writers have begun to explore what CYA levels, if any, place swimmers in public pools at risk of contracting a recreational water illness due to a lack of active chlorine.

To be clear, most participants in this discussion are not advocating the elimination of CYA and the stabilized chlorine products it creates — trichlor and dichlor — in outdoor pools. Instead, new or revived information about the relationship between CYA and chlorine has left them to wonder if current standards, codes and best practices allow levels that are too high.

On the home front

Until recently, the industry did not place too much emphasis on the effects CYA has on the ability of chlorine to do its job.

But a few years ago, industry chemist and the author of the manual, Robert Lowry, started exploring why pools with proper free chlorine levels would have algae problems. He came to conclude that CYA's impact on chlorine efficacy was a culprit, through his examination of existing studies and conversations with various scientists, including one who has entered the industry recently but attained a high profile relatively quickly.

Richard Falk holds undergraduate degrees in chemistry and physics from University of California, Berkeley but, after earning an MBA, had spent most of his career in computer science. He became interested in CYA and pool chemistry because of algae problems in his own backyard pool. After participating in online forums and revisiting old research, he had also come to believe that high ratios of CYA to free available chlorine were a source of the problem.

Falk now is a key member of a special group within the Council for the Model Aquatic Health Code (CMAHC) charged with researching and determining what the model code should say about CYA and its place in a commercial pool’s regimen.

Lowry went on to perform more research and conclude that it was not enough to ensure pools have 1 to 4 parts per million of free chlorine. Instead, he says, the levels should be at least 7.5% of the amount of CYA in a pool. He used this information to formulate a new maintenance regimen for residential pools, which he and his late business partner, Greg Garrett, have taught through the Pool Chemistry Training Institute.

Lowry and IPSSA also updated the Basic Training Manual, adding to the section on CYA and stating that “Having 30 ppm CYA in the water lowers kill times by a factor of at least 15 to 30.” He recommends that CYA levels top off at 50 ppm, which would require a free chlorine level of 3.75 ppm. Because CYA builds up quickly from trichlor, he recommends against using it as the pool’s main source of chlorination.

However, he isn’t proposing the elimination of CYA. In fact, in the latest edition of the IPSSA Basic Training Manual, Lowry lists the beneficial aspects of CYA — it keeps chlorine in the water eight times longer; it acts as a buffer against pH reduction — as well as its challenges. “That’s pretty impressive for a single chemical,” it concludes.

The commercial side

On the commercial side, the Centers for Disease Control and Prevention has also taken an interest in CYA, at least in part because it oversees the Model Aquatic Health Code (MAHC). While it doesn’t encourage or discourage use of cyanuric acid, it does recommend a minimum free availability chlorine level of 2 ppm in pools sanitized with stabilized chlorine, versus 1 ppm without.

The Council for the Model Aquatic Health Code (CMAHC) took up the issue of cyanuric acid levels in public swimming pools, as some members became concerned about CYA’s effects on the efficacy of chlorine and, specifically, its impact on the active form of chlorine, hypochlorous acid (HOCl).

In 2017, while producing the latest MAHC update, the organization considered tackling the CYA question. Instead, it created the ad hoc committee, in which Falk is a key member, to determine how much CYA could be present while leaving enough active HOCl to keep up with the introduction of pathogens in water populated by many people in public venues.

The ad hoc committee is comprised of representatives from both chlorinated isocyanurate and calcium hypochlorite manufacturers to ensure that financial interests of one could not sway the outcome. Some academics rounded out the team.

The group plans more studies in the future, but this round, it examined how high the CYA: FAC ratio can get before compromising chlorine’s ability to combat transmissions through regular fecal sloughing. This means fecal matter that washes off a person of normal health who doesn’t have diarrhea.

The committee intends to investigate appropriate doses for accidental fecal release in the future.

For this study, the team looked at existing data and previous studies. It also developed models, similar to software calculators where inputs can be applied to learn their effects.

The committee’s findings, published in the peer-reviewed journal Water, break down into two main parts, says Falk, who recently founded WaterGuru, a Menlo Park, Calif. maker of smart products that monitor and dose chemicals in residential pools.

The first part of the findings address the relationship between chlorine and CYA. Currently, most or all pool codes and standards stipulate limits for free chlorine and CYA that are independent from the other. The Model Aquatic Health Code, for instance, currently requires a minimum of 2 ppm chlorine and a maximum of 90 ppm CYA. This does not account for the relationship between CYA and HOCl, specifically how the former impacts availability of the latter. By applying the most extreme parameters allowed by each code or standard, the committee determined that HOCl levels can vary by a factor of 500, depending on the combination of CYA and free chlorine levels. That means one set of parameters can yield HOCl levels that are 500 times less than another, and vice versa.

The committee sought to substantiate the relationship between CYA and free chlorine in maintaining HOCl levels. It also sought to find out how free chlorine levels compared with HOCl levels as an indicator of effectiveness at combatting pathogens.

One way the team did this was to take three studies examining Streptococcus faecalis, looking at how the concentration of the bacteria was reduced by free chlorine versus HOCl. When plotting out the effectiveness of these different components — free chlorine and HOCl — the team found more consistency in the performance of HOCl. The difference was even more drastic when looking at the correlation between HOCl and Cryptosporidium reduction versus that of free chlorine.

“When people go into the water and they have high free chlorine levels, they think, ‘Oh, everything’s okay.’ But that’s not necessarily true,” Falk says. “If you have a higher CYA level and a lower free chlorine level, you will have a lower HOCl level, and there could be a risk of a problem.”

Results from another part of the model showed consistent HOCl levels when the ratio of CYA to free chlorine was the same, regardless of how high the parameters reached (within the limits of current code). When the CYA was approximately 20 times higher than free chlorine, it would yield a similar HOCl level.

This helps operators and service techs solve a testing problem, Falk says. “We know we want to measure HOCl, but how do you do that when you can’t do that directly [through current tests]?” he says. “It turns out you don’t have to. If you know the CYA and free chlorine levels... if you had a constant ratio, the HOCl is nearly constant.”

Other findings suggested that CYA more significantly affects HOCl concentrations than does pH.

Proper ratio

The committee also sought to determine the optimal ratio of CYA to free chlorine.

The members explored this issue in a number of ways. One was to measure at what point the risk of giardia becomes unacceptable. They chose this condition for two reasons: It is most prevalent in the population at large, and people infected with it show higher concentrations of the pathogen in their fecal matter.

Employing the model, they charted the probability of children becoming infected with various pathogens, including giardia, at different CYA-to-free chlorine ratios. After approximately the 20:1 mark, the projected risk surpasses that allowed by the U.S. EPA at beaches and other venues with untreated recreational water, based on fecal bacteria measurements in the water.

With this finding, along with other research and considerations, the committee recommended a 20:1 ratio of CYA to free chlorine.

Not everybody agrees with these findings. And the 20:1 ratio recommendation has a road ahead before it can become codified. A future issue will cover reactions to CMAHC’s study and other changes regarding CYA, as well as what they mean for future standards.

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