Cyanuric Acid - The Ultimate Guide

Cyanuric Acid (Stabiliser) in Pools - What Does It Do?

Cyanuric acid is a vital component of any outdoor pool’s chemistry.

Although it is much less frequently discussed than other chemistry factors like your pool’s chlorine and pH levels, maintaining ideal levels of cyanuric acid in your pool is essential for keeping these other chemicals in balance.

In this in-depth guide to cyanuric acid, we will discuss what this acid is, how it is used in pools, and other names that you may see it referred to as.

We also cover the ideal levels of CYA for your pool, how you can test these levels, and the problems associated with both low and high levels.

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Cyanuric Acid For Pools

Pool cyanuric acid is a chemical product that is used to protect your water’s chlorine molecules from the sunlight.

Chlorine molecules are very fragile when exposed to the sun and therefore degrade quickly during the day under normal conditions. However, when protected by cyanuric acid, chlorine molecules resist this degradation process and last much longer.

Chlorine is added to swimming pools as a sanitation product, and is a constant source of ongoing maintenance costs for most pools. In ideal conditions, your pool’s chlorine gets used up as it kills microbes that are present in your water.

However, if you do not have enough of this essential cyanuric acid in your pool, a large majority of the chlorine that you purchase for your pool is going to waste.

Other Names For Cyanuric Acid

Cyanuric acid for pools is also known by a couple of other names. It is commonly called pool stabiliser, which refers to the protective effect that it has on the chlorine molecules in your water.

You may also see cyanuric acid abbreviated as CYA, which is typically capitalised. All of these terms refer to the same product.

Is Cyanuric Acid Safe To Handle?

Although high cyanuric acid will make your chlorine ineffective and cause unsanitary conditions, this product itself is not harmful to humans in its diluted form.

In the form of a dry acid, or as a liquid solution, concentrated cyanuric acid can be harmful if it comes in contact with the skin or eyes, or if it is swallowed. This acid is not nearly as corrosive as others, such as hydrochloric acid, but it is best to practice caution.

If the dry form of this acid is used, extra care should be taken to ensure that dust from this product is not inhaled, as respiratory irritation can occur and may lead to lung damage in some people.

If using the liquid form of this acid, it is advised that you use it in a well-ventilated area, as exposure to fumes can have similar effects.

If dry or liquid cyanuric acid comes in contact with your skin or eyes, rinse the area thoroughly with fresh, running water. In case of accidental consumption of this product, seek emergency medical attention immediately.

Ideal Cyanuric Acid Levels For Pools

Ideal levels for stabiliser in your pool range from 30-50 parts per million (ppm).

If you use a stable form of chlorine for your pool, such as dichlor and trichlor, these products already contain some CYA, so you may have more stabiliser than you think.

I actually don’t recommend using stabilised chlorine, as it becomes difficult to control stabiliser levels independently of chlorine levels.

It is better to use non-stabilised chlorine (such calcium hypochlorite or liquid chlorine) for your regular pool maintenance.

Both low cyanuric acid and high cyanuric acid can render your chlorine ineffective and lead to algae and bacteria outbreaks, so it’s important to keep your stabiliser concentration within the recommended range.

How To Test Cyanuric Acid Levels

In order to test your cyanuric acid levels, you will typically need a unique test kit for this purpose. Most multi-purpose dip-strip chemical tests do not include a test for CYA, so you will need to obtain a specific solution-based testing kit.

To test your stabiliser levels using a test kit, fill the vial with the appropriate amount of pool water, and then add the required amount of testing solution. Invert the testing tube if indicated by your test kit’s instructions.

When the results are ready, compare the colour of the solution you mixed with the colour chart provided by the test kit manufacturer in order to determine the approximate level of CYA in your pool.

Problems Caused By Low Cyanuric Acid

The most common problem caused by low cyanuric acid in your pool is increased and rapid chlorine consumption.

Because the stabiliser protects free chlorine molecules from degrading in the sunlight, pools with little to no CYA tend to use up much more chlorine during the course of a normal day.

When your chlorine levels drop rapidly, this gives microorganisms in your pool like bacteria and algae a chance to flourish and begin spreading. For this reason, pools with low CYA are more likely to develop unsanitary conditions.

Many pool owners try to combat these unsanitary conditions with more chlorine, but without the stabiliser present, this process can get very costly.

If your pool requires lots of chlorine to be added regularly in order to maintain ideal levels, it is likely that you have low cyanuric acid levels. To learn more details about this condition and how you can remedy it, check out our article on low cyanuric acid in pools.

How To Raise CYA In Your Pool

In order to raise the amount of cyanuric acid in your pool, you will need to either use a stabilised form of chlorine or add stabiliser directly (which is what I recommend).

Stabilised chlorine products are typically sold by the names trichlor and dichlor, and come in different forms.

Most pool owners prefer to use stabilised chlorine tablets in a floating dispenser, and these are sometimes also suitable for use in skimmer baskets depending on the specifications of your equipment.

You can also add stabiliser to your pool directly. Liquid forms of this product are available, as well as powdered forms. Once you have figured out how much product to add to your pool, this product can simply be added to your skimmer box while the pump is running.

How Much Stabiliser To Add To Pool

To calculate how much stabiliser you should add to your pool, you can use this handy calculator.

To use the calculator, you will need to know the volume of your pool and your current CYA levels. You can then set a desired level for CYA and select the product of your choice to find out how much product you should add.

Problems Caused By High Cyanuric Acid

When cyanuric acid levels in your pool exceed the recommended maximum levels of 50ppm, they begin to cause problems with your pool. At these levels, cyanuric acid reacts with so much of the chlorine that it actually becomes ineffective.

These ineffective chlorine molecules are unable to kill off any active contaminants in your pool.

Chlorine ineffectiveness then leads to the same problems as low chlorine levels, which include algae infestations and an abundance of bacterial growth in the pool among other unsanitary conditions.

How To Lower CYA In Your Pool

The most common way to reduce the amount of cyanuric acid in your pool is by draining and refilling a portion of your pool’s water. This should only be done in small batches until a better level of CYA is reached, as draining too much water at a time can lead to pool-popping.

We recommend draining your pool to no more than 7cm below the normal water line before replacing this amount with fresh water. After doing this, allow your pump to circulate for a couple of hours before retesting your stabiliser levels.

Use this calculator to work out how much water to drain and refill.

Other remedies to high cyanuric acid levels are available, although their effectiveness is yet to be proven. Enzyme-based CYA removing products are a new solution for this problem that is rising in popularity as they are capable of lowering the stabiliser levels in your pool without draining.

These products can be somewhat complicated to use because they contain bioactive elements, so it is important to follow all instructions on the product’s packaging related to your pool’s chemistry levels and ideal water temperature before use.


Cyanuric acid, sometimes called pool stabiliser or abbreviated as CYA, is an essential component of any outdoor pool’s chemistry.

This product is necessary to protect your pool’s chlorine from breaking down in the sunlight, which can quickly deplete your chlorine levels if you aren’t careful.

Although it is necessary to have, at too high levels, cyanuric acid can become a bad thing. It can render chlorine ineffective at sanitation, allowing bacteria to develop in your pool.

Do you have any questions about cyanuric acid for pools or how it is used? Get in touch with us through the comment section, we’d love to help!

Louis from Pool Advisor


A chemical engineer by trade, Louis is committed to debunking myths in the pool industry by explaining the underlying chemistry and making it accessible to all.