cyanuric acid, CYA, problems with cyanuric acid, how to remove cyanuric acid, reduce cyanuric acid, lower CYA

Five things you need to know about Cyanuric Acid

Five things you need to know about Cyanuric Acid

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.


As mentioned earlier, CYA stays in the water for a long time. The easiest and most affordable way to reduce cyanuric acid is to drain the pool—at least partially. There are some products that can reduce CYA as well, but like any chemistry, there are reactions for every action. We won’t get into the weeds on the chemistry, but if you would like to learn more, we encourage you to research how to lower cyanuric acid levels.

Misleading reading

ORP probe, cyanuric acid, cyanuric acid confuses ORP

An ORP probe

Let’s talk briefly about how ORP sensors and test kits can be fooled by cyanuric acid. Increasing cyanuric acid lowers ORP. Yet, if you measure free available chlorine on a DPD test kit, the chlorine shows up as free available chlorine (FAC). Why the inconsistency in results? We can explain.

ORP stands for oxidation reduction potential. ORP sensors are probes that instantly measure the conductivity (in millivolts, mV) of water. They sense chlorine, but not chlorine attached to cyanuric acid. As a result, ORP may be lower, even if free chlorine remains the same. So what will the pool chemical controller do when the ORP levels are too low? Add more chlorine. Sometimes it takes additional calibration of the controller and sensors to get things operating right. This is something to be aware of if you have chemical automation.

4. The Federal Government regulates CYA levels

What is the limit for CYA? Well, according to the US Centers for Disease Control (CDC), it’s 15 parts-per-million. Specifically, in the event of a fecal incident, the pool’s CYA level cannot exceed 15ppm. But do you know of any neighborhood summer pools that can get through their entire season without a single fecal incident?

Better to be safe and prepared than be shut down by the health department. From the CDC: In case of a fecal incident, close the pool, and CYA levels can no longer exceed 15ppm.

Why the CDC CYA limit happened

It’s very simple: chlorine stabilizers (like CYA) slow the rate that free chlorine kills pathogens. In the event of a fecal incident, sanitation is paramount to quelling diseases like cryptosporidium. CYA just gets in the way.

Let’s get real here. If you’re treating outdoor commercial pools, keeping CYA under 15ppm is really hard to do. We get it. But that’s not an excuse for ignoring the CDC’s mandate. So what can we, as industry professionals, do to comply with this new CYA regulation? It’s our opinion at Orenda that the CDC’s 15ppm limit—while it is a painful change for many—offers an opportunity for new thinking. Pools have been operated the same way for so long; changing the way we think about water can be a good thing.

5. CYA can remain even after you drain

We have heard numerous first-hand stories of draining high cyanuric acid pools. For example, a service tech had a homeowner with a pool over 100ppm CYA. Drained the pool completely, and refilled it.  Without adding anything to the pool yet—besides tap water—the CYA level was 30ppm the next morning.

We did some research. In not-so-scientific terms, we interpret the findings to mean that some CYA can stay behind when draining a pool. It can deposit itself on the pool surface as the water drains, and wait to be reabsorbed when refilled. We are not sure what it looks like or feels like, but it explains the mystery CYA in a newly refilled pool. Could it be that CYA is left behind like salt or other minerals? It seems possible…but we will continue to look into it. If you’re a chemist or cyanuric acid expert, please weigh in and contact us. We’d love to know more about it.

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The most misunderstood chemistry in the pool business


Calcium impacts all types of pool surfaces

Pick your surface, fielder’s choice: plaster, pebble, tile grout, fiberglass/gelcoat, or vinyl. What do they all have in common?  They are all—without exception—dramatically impacted by the calcium hardness level in the water.  This article will attempt to explain the urgent need to understand and manage proper levels of calcium hardness in our pools.

Having begun my career in the pool service industry in 1984, I have a confession to make. Call it an admission of guilt. A common belief–which I shared–was “I do pool repair, not chemicals”.  This is more common than not, so let’s explore why it’s a problem. How many of us pool repair people even bothered to carry a pool chemical test kit on our truck? Not me. How about calcium chloride? Nope, me neither.

Alright, so you say “That is not true! I have a 4 in 1 test kit to check the pH.” And maybe if you’re feeling generous, you checked the chlorine and alkalinity too. Well guess what: when you discovered a hole in the heat exchanger, if your instant conclusion was just “low pH”, think again. I used to think that, and I was painfully mistaken. At the expense of my customers.

Water chemistry is very dynamic and constantly changing.

The measurement you get at one moment may have nothing to do with the current condition of your surface or equipment. It is more likely that a water balance problem presented itself over a long period of time; not the moment you are testing the pool. Furthermore, the most important overriding chemical question was “what was the LSI reading?

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Simply raising the calcium changes the LSI significantly.

On this illustration of our LSI Calculator App, notice the only difference in the chemistry between the right and left levels is the calcium level. All other measurements are identical. The difference between a pool that is corrosive or not simply relies on a higher calcium hardness level.

By the way, the aggressive reading on the left of the screen has a industry-acceptable level of 200ppm Calcium Hardness. And we all thought we were within range.

Another benefit and point of fact about calcium hardness is that it is very slow to change, and less dynamic than pH or alkalinity.  What would you rather control first? A chemistry that fluctuates by literally minutes or hours (pH and alkalinity)? Or one that is very stable and slow to change (calcium hardness)? In my opinion, it’s a very easy decision.

LSI first. Range chemistry second.

So why does the industry generally regard calcium as a detrimental chemistry? We instantly assume it will cause scaling at most levels. Why? Because we have been taught to think so. But in reality, the truth about scale and corrosion lies with the balance of the LSI, not just calcium. In my view, the LSI is the primary measure of balanced chemistry, not range chemistry.


This is a very critical point, so let me repeat myself. LSI first. Range chemistry second.

How may times have you heard someone say “But my pool chemistry is good”?  Perhaps the chemistry is in proper ranges acceptable to the industry. But as the earlier screenshot shows, so much for “good pool chemistry”.  Bye bye to the plaster and equipment over time. By simply elevating the calcium level we can protect equipment and surfaces.

Water stops at nothing to find balance

So you say to yourself “But Harold, I treat vinyl liner/fiberglass pools…the surface is not at risk.” Wrong. Both surfaces are impacted identically to a plaster pool with one exception. Neither vinyl nor fiberglass has available calcium to donate to the water like a plaster pool. That is to say, in calcium deficient water, a plaster surface gives up necessary surface calcium to attain equilibrium with the water (causing premature surface failure).

So yes, liner and fiberglass pools may not etch the way plaster does, but they will degrade.

Equally important to note: surface degradation is gradual and will escape visual evidence for quite some time…perhaps leading you to believe there is no damage taking place.

Low calcium water in vinyl or gelcoat/fiberglass surfaces continues to create more corrosive water. There is no mechanism to improve the buffering power of calcium and will therefore cause plastic to become more brittle and gelcoat to chalk and degrade or etch. Truth be known, vinyl liner and fiberglass pools are likely to decline faster in a low-calcium environment.

Is high calcium hardness always a problem? No.

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If other factors are adjusted properly, 500ppm calcium hardness is easily managed, without scale formation.

Look at the screenshot of our LSI calculator. I show you this to burst the myth that 500ppm calcium hardness is always scale forming, and therefore a problem. We have been taught for so long that we must drain the pool to correct high calcium hardness. I argue that’s not necessary.

My question to the industry is a simple one: do you take issue with the LSI or not?

The LSI standard is cut and dried. So if the LSI is balanced—which by the way, at 500ppm on our calculations, it is—what are we to think?

If the LSI is the Gold Standard for corrosion and scale formation it seems to me it should trump a range guess of balanced water.

Pool chemistry and balance is always changing

Remember when I stated previously that water chemistry is dynamic and constantly changing? Take that into account in this conversation…the LSI can change day to day, week to week. Manage the water chemistry accordingly. One can assume in the course of a week, the pH in a plaster pool will rise, and in vinyl or fiberglass pools the pH will drop in most cases.

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Most of the etching and corrosion that takes place in the pool occurs during the winter. Why? Temperature is a critical factor in the LSI.

Lastly be VERY AWARE of the water temperature! Water temperature has a dramatic impact on the LSI. This will be discussed in a later article at length. It was a painful epiphany for me as a service professional of 30+ years. Play around with the temperature dials on our app and brace yourself for some brutal truth.

Conclusion: Calcium Hardness is your friend

In conclusion, I hope this information has been helpful. I encourage you to use our Orenda App to always test and measure LSI balance. Never guess, or base your actions on old habits.  Lastly, maintain a minimum of 200ppm calcium within 24 hours of filling a pool, and use the great asset of calcium hardness as your friend—not your enemy.  Help me change the negative view of calcium hardness levels and use it to our advantage as the positive factor it is.  Together we can change the way the world treats and thinks about water.

Harold Evans began his pool service/repair company, The Pool Surgeon, in 1984. Frustrated with problems he could continue to fix–but not prevent–he searched for a water chemistry solution to resolve many of the problems he faced as a pool professional. Harold is now the CEO/owner of Orenda Technologies, and focuses on educating pool professionals on how to make the swimming pool safer, long-lasting and enjoyable for all.

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