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.
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.
