When it comes to operating and managing swimming pools, disinfection is king. It’s a requirement for Health Departments, municipalities, counties, and states everywhere. By far, the vast majority of outdoor pools operating in the US use chlorine as their primary disinfecting agent to kill and control bacteria, viruses, algae, and other microscopic contaminants. 

But while disinfection may be your primary objective, there are several other qualities that make pool water safe, healthy, and swimmable–and a number of other pool chemicals that are just as vital. One of those for outdoor pools is cyanuric acid, also referred to as pool stabilizer. Without it, the chlorine you add would be consumed by the sun in a matter of hours. And just like chlorine and any other pool chemical, there’s a specific range cyanuric acid needs to be maintained at.

So, if you’ve performed a routine chemicals test and found the cyanuric acid low in pool water, what do you do? Let’s dig into why that may happen and how to remedy (and prevent) it. 

Reasons Why Cyanuric Acid May be Low

The CDC recommends that all aquatic venues using chlorine and cyanuric acid (CYA) as a pool stabilizer should maintain a minimum DPDFC concentration of 2.0 ppm. The CYA binds to chlorine molecules, creating a protective layer that prevents them from being prematurely degraded by the sun. 

It does this while still allowing the chlorine to disinfect pool water, making it a powerful partner to chlorine. However, you also want to keep CYA below 40-50ppm. Once you get above that range, it doesn’t give you any extra benefit or protection against chlorine degradation and it can also begin to cause issues. 

You can add cyanuric acid and chlorine to pool water in one of two ways:

1. Stabilized chlorine: stabilized chlorine (Dichlor and Trichlor) is sold in a tablet form (hockey pucks) with the cyanuric acid already added, thus making it stabilized. This is a convenient form to use in your pools, but it doesn’t give you the best degree of control over each individual chemical level. Over time, the chlorine still degrades, requiring you to add more, but the CYA does not. This means that if you’re adding a stabilized chlorine tablet each time, you’re gradually increasing your levels of CYA. This can lead to something called “chlorine lock,” which happens when CYA levels are too high and prevent the chlorine from doing its job. Fixing chlorine lock typically requires draining the pool and refilling it with fresh water and chemicals.
   
   
2. Unstabilized chlorine + cyanuric acid: You can also add chlorine on its own, called unstabilized chlorine, (Cal-Hypo, liquid Sodium Chloride) and add cyanuric acid separately. This allows you to have more control over each chemical’s levels and ensure you’re always adding the right amount of each, preventing chlorine lock while still stabilizing the chlorine. 

We highly recommend using unstabilized chlorine, and adding the CYA separately. However, ensure that you or staff are properly testing all chemical levels and adding the appropriate amount of cyanuric acid. One mistake that can lead to low cyanuric acid levels in pool water is using unstabilized chlorine, without the CYA–or thinking you’re adding stabilized chlorine, but instead, using unstabilized. 

Other reasons why cyanuric acid may be low in pool water include:

• Heavy rainfall or large storms,
• Backwashing, 
• Over Dilution, such as from draining and refilling pool water too often, 
• Heavy splashout, such as from large, rowdy parties. 

In other words, anytime pool water gets sufficiently diluted enough, the result will be imbalanced chemical levels, including cyanuric acid levels.

What Happens if Cyanuric Acid Levels are Low?

There are a few issues that can result from too low CYA levels. As we mentioned, the sun will degrade chlorine at a far faster rate, and will reduce disinfecting ability. If you don’t catch the low CYA levels quickly, you may find yourself adding chlorine at a faster rate, increasing chemical expenses, while also risking disease spread and Health Department violations. 

This can also set off a chain reaction creating the opportunity for algae to grow rapidly. 

As the free chlorine gets used up rapidly, without enough CYA to protect it, it also binds to ammonia pollutants in the pool–including sunscreen and sweat–and creates chloramines, which creates a strong, unpleasant chlorine smell and can cause breathing issues, especially in indoor pools. 

How to Resolve Low Cyanuric Acid Levels

Once your test results reveal low cyanuric acid levels, calculate the amount you need to add to bring them back up into the ideal range. It’s important to add in more CYA slowly, as it stays in the water longer than chlorine and it is far easier to raise its levels than to bring them back down again. 

1. Once you have calculated how much to add, ensure the pool’s pH and total alkalinity levels are balanced and within the ideal range too. This will enable the pool’s chemicals, including the CYA you’re adding, to work at their most effective. 
2. In general, we recommend adding cyanuric acid separately, rather than adding in a stabilized chlorine tablet or granules that contain both chlorine and CYA. As we mentioned before, it is far easier to maintain control over the stabilizer’s levels this way. If you are using stabilized chlorine the cyanuric acid levels are going to be raised over time so you may not want to add more to the water.
3. As a rule of thumb, approximately 13 ounces of cyanuric acid will raise a 10,000-gallon pool’s stabilizer levels by 10 ppm. If you’re using the PoolShark H20 app, the app will automatically calculate the precise amount you need to add based on your water test results.
4. Proceed carefully when handling cyanuric acid as it is an acid. Splashback when pouring the chemical can cause skin, eye, and lung irritation and even chemical burns. As with all chemicals, the best method is to start with a bucket of water, and pour the acid into the water to dilute first. This will reduce the risk of splashback and diluting first also helps protect the pool’s lining and surfaces.
5. Pour the diluted CYA into the pool and run the pump for several hours to allow it to circulate.
6. Retest water again, and if stabilizer levels are lower than expected, you can add more. Again, it’s important to add small amounts slowly as raising CYA levels too high will require draining the pool by several inches, adding in new water, and continuing to adjust until water is rebalanced. 

Final thoughts on Cyanuric Acid

Cyanuric acid, or pool stabilizer, ensures chlorine’s ability to disinfect pool water effectively without quickly being degraded by the sun. When cyanuric acid levels are too low, chlorine will be destroyed by sunlight quickly, potentially resulting in reduced water safety and potentially cloudy, smelly, and irritating water. Raising CYA levels also takes a careful hand, along with precise calculations to ensure pool water as a whole is balanced and healthy, while CYA is raised back up to within the ideal range. 

It’s precisely scenarios like these that we designed the Pool Shark H2O app for. Using the app ensures pool water test results are logged quickly and accurately, and because it performs the complex pool chemistry calculations for you, it removes a high degree of human error from this process–ensuring you or pool staff gets chemical amounts right the first time, and helping you reduce chemical waste, and the extra costs that go with it. For pool managers and owners, records can be viewed remotely from anywhere and because you’re notified when tests are missed, aren’t run, or there are issues, you can be sure pool water is safe and attended to promptly, and your logs are always Health Department compliant.