Cyanuric Acid (CYA) and How it Impacts Chlorine | Orenda Whiteboard
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Cyanuric acid (CYA) is well known in the pool business. It serves as a protection shield for chlorine against sunlight. The Sun’s ultraviolet rays degrade chlorine very quickly, creating a problem for outdoor pools. Studies show that sunlight can be wipe out chlorine by 75-90% in a matter of two hours. The half-life of chlorine—when exposed to direct sunlight—is about 45 minutes. That means half your chlorine is gone in 45 minutes. Another 45 minutes, another half of your chlorine is gone. So on and so forth.
A chlorine stabilizer is needed, otherwise you will be using (and losing) chlorine all day, every day. Chlorine used to be added daily up until the discovery of cyanuric acid in 1956. This article will outline a few things you should know about cyanuric acid.
1. How cyanuric acid works
The cyanuric acid molecule is a hexagon with alternating Nitrogen and Carbon atoms. It allows for three molecules of chlorine to attach to the nitrogen, forming a weak nitrogen-chlorine bond (N-Cl). Because the N-Cl bond is weak, it allows for chlorine to let go of CYA when it has something to oxidize or kill. When attached to CYA, however, chlorine is protected from sunlight. Cyanuric acid is kind of like sunscreen for chlorine.
We know the Nitrogen-chlorine (N-Cl) bond is weak because the chlorine attached still shows up in a free chlorine test. If the bond were stronger—like that of chloramines and other disinfectant byproducts—chlorine would only show up on a total chlorine test, not free chlorine.
A metaphor: Imagine a floating raft that chlorine holds onto. When it needs to leave the raft to oxidize or kill a germ, chlorine simply lets go of the raft…and another chlorine molecule will take it’s place and grab the raft. As long as chlorine is holding onto the raft, it’s protected from sunlight. When it lets go, it’s active free available chlorine, but vulnerable to sunlight.
Cyanuric acid is available as a granular solid and as a liquid (sodium cyanurate). Most commonly, however, cyanuric acid is found in stabilized chlorines dichlor and trichlor. These stabilized chlorines have about 50-58% CYA in their formulas.
2. Why use cyanuric acid?
CYA provides is a huge benefit to chlorine. CYA can extend the life of free chlorine by as much as 8 times in direct sunlight. For outdoor pools, that’s a game changer. That said, CYA is not to be used in an indoor pool.
Conventional wisdom in the pool business—at least, until recently—suggests an ideal range of CYA to be 30-50ppm, with a minimum of 10ppm and a maximum of 100ppm. Ranges vary, depending on state laws. We at Orenda recommend a little as possible (30ppm or less, ideally). Why do we differ? Because we recognize the need for chlorine to have longevity in sunlight, but also recognize its impact on sanitation. Additionally, with enzymes, chlorine levels can be minimal while maintaining a strong ORP.
Dosing a CYA properly is a matter of knowing how much free available chlorine (FAC) you want protected, and how many gallons of water are in the pool. It takes about 10ppm CYA to protect 1.5ppm FAC. You can use our dosing calculator app to figure out exactly how much you need.
When water evaporates, CYA stays behind. Because of that, cyanuric acid stays in the water for a long, long time. This can be considered a benefit for some…but it can also be a problem down the road. For the most part, CYA levels can remain very stable if you’re not adding more of it to the water. The problems occur when CYA levels get too high.
3. Problems with cyanuric acid
Weak chlorine
Since chlorine is the front-line defense against germs and diseases in water, weakening it is a bad idea. Not only does chlorine have to overcome the oxidant demand before sanitation can begin, there is approximately a 7.5% chlorine reduction factor with cyanuric acid. So let’s put this formula into the real world. If you have 100ppm CYA, you have effectively zero free available chlorine until 7.5ppm chlorine.