Managing Cyanuric Acid in Your Pool

What is Cyanuric Acid?

Cyanuric acid bonds to chlorine, giving it a protective shield against the sun’s U.V. rays. But it’s a double-edged sword for swimming pools. As a pool owner, know that cyanuric acid is not allowed in indoor swimming pools or spas, and that the city of Austin limits it to 100 ppm in outdoor pools.

Levels Too Low
With no cyanuric acid in the pool, the sun’s U.V. rays will burn off any free chlorine within minutes, leaving the pool vulnerable to algae and bacteria growth, both unsafe and unsightly. A lack of cyanuric acid also leads to the use of more chemicals in the pool to attach and kill the algae blooms or bacteria growth.

Levels Too High
On the other end of the spectrum, having extremely high cyanuric acid levels (above 50 ppm) is also bad. Even though we have protection against the sun’s U.V. rays, we also have a thicker layer of CYA (cyanuric acid) bonded to the chlorine. The higher the CYA levels, the thicker the layer around the chlorine. Why having a thicker layer of CYA bonded to the chlorine is a bad thing is because it actually slows down the rate in which chlorine can attack particles in the water, so much so that algae and bacteria can reproduce significantly faster than the chlorine can kill it.

Because of the slower kill rate that chlorine has with high CYA levels, it is required to keep the chlorine at 7.5 percent of whatever the CYA levels are. If CYA levels are at 100 ppm, then the chlorine level needs to be at a 7.5 ppm to be effective. Higher CYA levels = higher chlorine levels. This leads to a very uncomfortable pool to be swimming in. The high levels of CYA and high levels of chlorine leave the swimmer with dry, itchy skin and red burning eyes.

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Three different sizes of YardDoc Austin TX white chlorine tablets are arranged on a poolside with clear blue pool water in the background.

How Does it get in my Pool?

Given these issues, it is very important to maintain a proper level of CYA in the swimming pool. The most common place we find cyanuric acid is in the 3-inch chlorine pucks that most people use to sanitize their pool. A single 3-inch chlorine tablet weighs 1/4 of a pound and is 50 percent CYA per puck. That leaves us with an eighth of a pound of CYA per one chlorine tablet. This may not seem like a lot, but the thing with CYA is that it does evaporate off with normal evaporation. When your pool water evaporates off, roughly 1/4 inch per day, the cyanuric acid is left behind, causing CYA to build up over time. It is not uncommon here in Austin to see CYA levels reach well over 150-200 ppm, which is extremely high.

How to Maintain a Proper Cyanuric Acid Level

To stabilize a pool that has low CYA, we add a desired amount of cyanuric acid to increase our level to 30-50 ppm, or whatever level we are trying to reach. To decrease CYA levels, on the other hand, is not so simple and takes more effort and more money. Take a look at our services and service area to see how we can help.


Drain the Pool

The first method to decrease our CYA levels is to drain a majority of the pool water and refill with fresh water. Depending on the location of your pool, there may be restrictions to draining the pool due to the chemicals in the water and where the water drains to. Also, draining a pool in Austin can get expensive depending on how many gallons are needed to refill and not to mention a huge obstacle if Austin is in a drought at the moment.


Add an Enzyme

The second option we have to decrease the CYA levels in the pool water is to add an enzyme that breaks down the CYA. This would be the ideal method since we don’t have to worry about draining or drought restrictions. This method takes several trips to the pool throughout the course of a week to make sure certain chemicals stay within range to ensure the enzyme is able to work properly and break down the CYA.

The one thing to consider with both of the options is that it is likely that a pool with high amounts of CYA build up, left for years without treatment, has allowed the CYA to leach into the plaster.Therefore creating a need for pool resurfacing.


After either one of these methods has been applied, it can happen that the CYA that has leached into the plaster over time actually starts to leach back out into the water causing the CYA levels to increase over the period of a month, meaning that a second treatment would be needed.

It is impossible for pools that use chlorine pucks as their main source of sanitation to avoid a cyanuric acid problem over time. In fact, it is inevitable.

The ideal solution to prevent this from happening is to install a Pentair Intellichem system that would dose liquid chlorine. Liquid chlorine has no CYA added to it, and when introduced into pool water, goes to work immediately.

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