CYA – Cyanuric acid (AKA Stabilizer)

What is Cyanuric Acid (CYA)?                             

Cyanuric Acid, often referred to as “pool stabilizer” or “sunscreen for chlorine,” is a chemical used in pools to help chlorine last longer. Without CYA, the chlorine in your pool would quickly be broken down by the sun’s UV rays, making it less effective at keeping your pool clean and safe.

What Causes High CYA Levels?

High CYA levels usually happen due to two main reasons:

Many common chlorine products, like certain tablets or granules with tri-chlor and di-chlor contain stabilizer, or CYA. Every time these are added to your pool, more stabilizer (CYA) is added as well. The hotter the summer, the more chlorine you need, the more chlorine you use, the more the CYA rises with these products. Chlorine feeders are designed to utilize the stabilized chlorine 3” tablet for its highly compressed and slow dissolving characteristics.

Less Dilution: Unlike chlorine, CYA doesn’t easily break down or evaporate. As water is turned over either through splash out or evaporation, fresh water is added.  CYA remains in the pool and does not evaporate.  Over time, as you keep adding stabilized chlorine, CYA continues to build up.

Effects of High CYA:

When CYA levels get too high, it starts to affect your pool’s chemistry, most notably, your chlorine availability to sanitize your pool (Free chlorine).

Reduced Chlorine Effectiveness: CYA binds with the available chlorine in your pool, making it less effective. Many refer to this as “Chlorine lock.” This means you might have plenty of chlorine, but it’s not “free chlorine ” and it’s not working as well as it should, or at all.

Algae Growth: Because the chlorine is less effective, algae and other unwanted organisms can start to grow in your pool.

Cloudy Water: High CYA levels can contribute to cloudy or unclear pool water.


Remedies to Lower CYA:

Water Replacement/Dilution: The most straightforward way to lower CYA is to drain some/all of the water in your pool and refill it with fresh water. How much water to drain depends on your CYA reading and how many gallons of water your pool holds.  It’s always best to drain most all the water and refill with fresh water.



There are many factors involved in maintaining proper chemistry in a swimming pool.  Any of these factors can affect your pools need or demand for chlorine. 

  • Water circulation (Pump speeds and pump run times)
  • Proper filtration (Clean filter)
  • Pool usage (How often and how many people are using the pool?)
  • Pets (Are there dogs or other pets in the pool water?)
  • Exposure to direct sunlight (Sun burns chlorine)
  • Debris in the pool (Leaves and other organic debris)
  • Air and water temperatures


Final Thoughts:

We at Cactus Pool Designs are moving toward using a liquid chlorine product as a supplement to the tri-chlor stabilized tablet.  We will still fill your chlorinator with the tri-chlor stabilized tabs, but it is our intention to keep the tab feeder on a low setting and supplement the chlorine demand with liquid chlorine during our weekly visit.  Our goal in doing this is to minimize the elevation of CYA over the course of a summer.  This may not eliminate the rise of CYA in your pool, but it will certainly slow it down.

Non-Stabilized Chlorines: There is other non-stabilized chlorine in the tablet or granular form, and they have their own set of issues and precautions.  Non-stabilized chlorine tablets are not designed to be used in a feeder as it is not highly compacted and would turn to mush ruining your feeder, or worse, causing a chemical combustion.

Calcium Hypochlorite is the most common Non-stabilized chlorine for pool use and is roughly 60% chlorine while Sodium Hypochlorite in the stabilized tablet/granular form (Tri-chlor) is 90% chlorine.

Tri-chlor tabs are still the best and most efficient means to sanitize your pool.  We believe with the supplementation of liquid chlorine we can better control the rise of CYA and the need to routinely drain and refill the pool as a result.