![]() This gives you a target for free chlorine and makes it easy to know if you have enough free chlorine to provide safe water and prevent algae from growing. Unless you add more CYA, the free chlorine required will not change. Or if you have 50 ppm of CYA, you will need about 4 ppm of free chlorine (50 ×. As an example, you add 30 ppm of CYA and you will always need about 2 ppm of free chlorine (30 ppm ×. If you add CYA separately and then use liquid chlorine as the chlorinating source, the CYA will not change and you will always know what the free chlorine level should be (target). This is not hard to maintain or calculate. The recommended level of 2 to 4 ppm doesn't always work. ![]() The free chlorine level should be 7.5 percent of CYA.To help make sense of the issue, Lowry offers the following takeaways: The implications of the adjoining discussion are far-reaching. To that point, Lowry recommends rejiggering the standard to limit CYA concentrations to 50 ppm, meaning that when that level is reached it's helpful to switch to chlorine that doesn't contain CYA, sodium hypochlorite or calcium hypochlorite being the most commonly used.Īnd, at whatever the CYA concentration, FAC should be maintained at 7.5 percent of that concentration, i.e. "What the equilibrium equation tells us is simply that we need to think in terms of maintaining lower levels of CYA." "There's no question that in a chlorinated body of water exposed to sunlight, you need cyanuric acid," he says. While at first blush, this concept of the CYA/chlorine equilibrium might seem to demonize CYA and chlorine products that contain it, Lowry is quick to point out that without CYA in the mix, it's nigh onto impossible to maintain chlorine residuals because of how quickly chlorine is destroyed by UV light. "While algae itself doesn't present a health hazard per se, common sense tells us that if you're not killing the algae, you also might not be killing the bacteria." Simply put, we need to kill algae faster than it can reproduce." We don't need to kill everything's that in there, but instead prevent growth to the point that these organisms have no negative effect on bathers and water quality. "The basic idea is to determine how much chlorine we need to prevent growth. ![]() Coli, Pseudomonas, Giardia, Cryptosporidium or some type of algae? When you look at the required chlorine concentration for various organisms, the differences are huge," he explains. Given that there are potentially hundreds of organism species in a swimming pool, Lowry began exploring which of those should be used as a standard for the necessary levels of FAC at a given concentration of CYA. That led me to look at the level of chlorine we need to kill algae and bacteria." "Based on existing information," Lowry explains, "I came to realize that at any given time, you only have 3 to 4 percent chlorine available to do anything. (Lowry also cites chemist Ben Powell for first developing the 7.5 percent concept back in the '70s.) One of those came from an out-of-print book titled "The Chemistry of Water Supply, Treatment and Distribution" by Jay O'Brien (Ann Arbor Publishing, 1973). "He told me that some of the information in the manual was incorrect, especially where CYA and chlorine are concerned."įalk shared with Lowry a number of citations to support his critique. "I received a correspondence from theoretical chemist Richard Falk," he recalls. Lowry's re-examination of the CYA/chlorine relationship began as a result of his authorship of the Independent Pool and Spa Service Association's two chemical training manuals, which he wrote in 20 respectively. The relationship between CYA and chlorine is one of those assumptions." "Sometimes that means challenging our basic assumptions. "I've always tried to share information with the industry that I believe to be true," he says. Lowry's seminars on water chemistry in pools and spas are widely considered the gold standard for water treatment education within the industry.
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