What is Cyanuric Acid in Pools

Cyanuric acid (CYA)  serves as a protection shield for chlorine (Cl) against sunlight. The Sun’s ultraviolet rays degrade chlorine very quickly, creating a problem for outdoor pools. Studies show that sunlight can wipe out chlorine by 75-90% in a matter of two hours so this is a critical monitoring test.  What is cyanuric acid in pools?

Cyanuric acid (CYA) combines with free chlorine (FC) in pools protecting it from the sun’s ultraviolet rays and reducing chlorine loss when properly managed at 30-50 ppm maintaining a minimum Cl residual in outdoor pools but above 50 ppm CYA reduces the overall effectiveness of Cl & needs to be reduced.

Cyanuric Acid is like sunscreen for your pool water’s chlorine. Much like your skin, chlorine particles are sensitive to the sun’s UV rays and when the rays hit chlorine particles, they destabilize, break apart, and subsequently evaporate out of the pool water. Cyanuric Acid like a strong SPF on your skin, Cyanuric Acid binds to the chlorine particles and protects them from the sun’s UV rays.


What is Cyanuric Acid in Pools


Cyanuric acid (CYA), also known as chlorine stabilizer or pool conditioner, is a chemical that helps stabilize the chlorine in your pool. It protects your chlorine from breaking down under the sun’s UV rays. The right levels of cyanuric acid help your chlorine last longer, which means your sanitizer can continue to kill bacteria, contaminants, and algae.

Having too little CYA  or too much CYA is a critical control that affects chlorine disinfection in a swimming pool.

The ideal range for cyanuric acid is between 30 and 50 ppm. Maintaining the right balance between cyanuric acid and chlorine is crucial for a sanitized pool. Too much cyanuric acid and your chlorine’s effectiveness decreases. Too little cyanuric acid and chlorine will break down under the sun’s UV rays. Where does cyanuric acid come from? Two of the most common chlorine products used for disinfection are dichlor and trichlor. Chlorine CYA chart, Cyanuric acid chlorine protection, CYA and chlorine sun protection

Dichlor and trichlor contain both chlorine and cyanuric acid so it is not necessary to add cyanuric acid to the pool water. Trichlor is about 55% CYA by weight.

Stabilizer (cyanuric acid) is also sold at most pool supply stores. Cal-hypo and liquid chlorine do not contain stabilizer

Try and keep free chlorine levels at 7.5 percent of cyanuric acid levels. If your pool has CYA levels at 50 ppm, you’ll need to keep your free chlorine levels at 3 ppm to effectively sanitize your water. In general, your pool water-free chlorine should be between 1 ppm and 3 ppm.

CYA keeps the chlorine in the water up to eight times longer. Pools that need a daily dose of chlorine added now only need chlorine once a week with CYA. Chlorine (CL) in the water quickly binds to CYA and a smaller portion of the chlorine is available.

The chlorine is around longer, but it does not kill as quickly. And as the CYA increases, there is less and less chlorine available for killing bacteria and microorganisms.

Innovative chlorine manufacturers in the late 1950s started combining chlorine with CYA to make chlorinated isocyanurates called dichlor and trichlor. Trichlor tablets quickly became the most popular chlorinating product for pools.

But having too much or too little cyanuric acid in your pool can reduce your chlorine’s effectiveness and even damage your pool equipment. Here’s everything you need to know about how cyanuric acid works with chlorine and how to raise or lower your cyanuric acid levels.


Cyanuric Acid Reducer


By forming temporary binding with the (FC) free chlorine, cyanuric acid will reduce the overall effectiveness of chlorine. As the level of cyanuric acid rises, free chlorine’s ability to act as a disinfectant is weakened. The amount of time it takes to kill bacteria lengthens as the concentration of cyanuric acid increases.

In the hot summers, the chlorine will be used up, however, cyanuric acid is never used up and accumulates in the pool water as a waste product. Once you have added it to the pool water, it will remain in the water. A maximum level of 100 ppm. CYA has been recommended by pool professionals.

 Sometimes high levels of CYA happen without you realizing it. Trichlor adds CYA every time you use it. As outside swimming pool water evaporates, CYA will stay behind, just like minerals calcium, and salt. If you are using a stabilized chlorine like trichlor or dichlor, CYA can accumulate quickly.  One pound of trichlor in 10,000 gallons of water will add 6 ppm of CYA.

Although these tablets dissolve very similarly to trichlor tablets, they cannot be used in trichlor feeders. Trichlor and cal hypo are incompatible and combining them can be extremely dangerous.

Ways to lower CYA are to:

  • Partially drain and dilute the pool with fresh water.
  • Use specialized filters– that will eliminate CYA  from pool water, such as reverse osmosis (RO). RO filters are expensive, but they may be the best option for people in regions of the country that are unable to drain their pools where water is expensive.
  • Use products like Bio-Active-that can reduce cyanuric acid levels by up to 50%  Eliminates chlorine lock due to a high cyanuric acid level


*Simply put dilution over time is often the best option. The alternatives to draining your water are to pay big money for filtration or try to manage the pool with high levels of CYA. Neither of those two options is as easy or affordable as replacing water with fresh water.

Try and monitor then keep CYA levels low enough to manage sanitation and maintain LSI balance. If your CYA is too high, draining and diluting is the most cost-effective means to reduce CYA in your pool.

Raise Cyanuric Acid Levels in Pools


The ideal range for cyanuric acid in your pool is between 30 and 50 ppm (parts per million). Anything lower and you will likely see some undesirable side effects when it comes to your water chemistry.

Raising your CYA levels can only be done 2 ways.

Before dosing your pool, however, it’s imperative that you test the pool water, and balance both the pH level and total alkalinity level beforehand. You can use test strips, a liquid test kit, or a digital test kit to find out where your pool’s chemical levels stand. CYA isn’t always a common testing parameter, use a reliable test kit.

  • Use a Stabilized chlorine like sodium dichlor or trichlor that is available in either powdered granules, liquid, or puck/tablets. All are easy to add to the pool and can be done in a few different ways. Granules can be mixed with water and poured into the pool, liquid chlorine (sodium hypochlorite) is also poured, and pucks can go either in your skimmer basket or a chlorine dispenser that floats in the pool.

There are also pool chlorinators that automatically feed the pool a set amount of chlorine, and you can use any kind of stabilized chlorine with them Adding pure cyanuric acid is another option. This method allows you to add it separately from chlorine, and will only need to be done once or twice a year at most.

  • Add CYA directly to the pool:
  1. Test and balance your pool H2O so you will know where your CYA level is and how much you need to raise it.
  2. Wear proper protective gear like eyewear, chemical-resistant gloves, and long sleeves with pants.
  3. Fill up a 5-gallon bucket with warm water.
  4. Measure out the correct dosage of CYA for your pool by checking the instructions on the product.
  5. Add the CYA to the bucket of water (never the other way around!).
  6. Pour the solution directly into the pool’s skimmer Slowly so you don’t clog the intake skimmer
  7. Allow time for the pool to fully cycle the water, distributing the CYA. Retest and repeat this process if more is needed.



Cyanuric Acid Pool Water Test Kit


The ideal cyanuric acid level for a salt pool is higher at between 60 and 80 parts per million (ppm). The CYA levels are higher in a saltwater pool than in a freshwater swimming pool.

This is because saltwater generators produce chlorine at a slow pace, which means they struggle to maintain an adequate chlorine level when large amounts are being burnt off by sunlight, especially at peak times of the day. As a result, it needs a little more protection than usual, putting the optimal ratio of free chlorine in a saltwater pool at no lower than 5% of the cyanuric acid level.

The first is a traditional liquid reagent drop test, such as those found in the popular Taylor testing kits. This is a very accurate test, but it’s fairly time and resource-intensive. The second is what’s known as the “black dot test”, made by Pentair.  This test is explained in the video. This isn’t quite as accurate as the Taylor test, but it only takes a fraction of the time to carry out and proves to be a lot more reliable than a test strip.

You should test your cyanuric acid (pool stabilizer) once per week until you have a firm understanding of your water chemistry. Once you begin to understand how your water reacts to natural and chemical changes, particularly in terms of your free chlorine level, you can reduce your CYA testing to as little as once per month.

*Use a reliable test kit like this one available on Amazon and recommended by MyWaterEarth&SkyTaylor Technologies K-1720 Pool Test Kit, which Tests Cyanuric Acid & Turbidimetric Acid Levels

*CDC recommends not using cyanuric acid or chlorine products with cyanuric acid in hot tubs/spas.

Unlike pH, alkalinity, or chlorine, in your swimming pool, your cyanuric acid level isn’t going to move very much over time, so unless your pool experiences massive water loss or heavy dilution, you can afford to carry out this test more infrequently.


JimGalloway Author/Editor




CDCPool Water Treatment and Testing




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