How To Lower Cyanuric Acid In Pool

Cyanuric Acid High In Pool - How To Lower It?

Cyanuric acid or stabiliser is an important chemical in your pool that contributes to the overall effectiveness of your sanitation products.

Because cyanuric acid is essential for outdoor pools and can prevent your chlorine from breaking down in the sun, many pool owners think about CYA with the perspective that ‘more is better’.

Unfortunately, when present in amounts that lie above the ideal range, stabiliser has various detrimental effects on your pool. If cyanuric acid is high in your pool, you will need to lower it to prevent any adverse effects.

In this article we will discuss the ideal levels of cyanuric acid or stabiliser in your pool, the symptoms of high cyanuric acid in pools, and how to test the stabiliser levels of your pool.

We also include advice for lowering the stabiliser content in your pool, as well as how to lower cyanuric acid in your pool without draining.

Ideal Cyanuric Acid Levels

Ideal cyanuric acid (CYA) levels in a swimming pool range from 30-50 parts per million (ppm), with 40ppm being considered the sweet spot.

In the correct amounts, CYA or stabiliser works to protect the free chlorine molecules in your pool from degrading in the sunlight, but like many other pool chemicals, CYA is subject to the law of diminishing returns.

This means that the effectiveness of your stabiliser does not continue to increase as its levels rise outside of the ideal concentration for swimming pools.

In fact, high levels of CYA require much higher levels of free chlorine than normal in order to maintain the same strength of sanitary effectiveness.

Symptoms of High Cyanuric Acid In Pools

While having low cyanuric acid in your pool can increase your chlorine consumption, high levels of CYA in your pool can have other undesirable effects. Symptoms of high cyanuric acid in a pool include false readings in other pool chemicals and an increase in unsanitary conditions.

When too much stabiliser is present in your pool, this reduces your chlorine’s effectiveness. If cyanuric acid works to shield the chlorine from sunlight, then you can think of too much CYA as shielding your chlorine from the rest of your water altogether.

As your chlorine becomes ineffective, bacteria and algae can begin to reproduce in your water. In addition to being unsanitary, ineffective chlorine can have other detrimental effects on your pool.

Ineffective chlorine caused by high CYA readings is typically also correlated with abnormal pH levels.

Cyanuric acid itself does not significantly alter the pH of your pool, but the conditions that result from ineffective chlorine can slowly cause your pool water to develop mild acidic properties.

An overabundance of cyanuric acid in your pool is also associated with incorrect readings in total alkalinity.

Your total alkalinity readings will tend to read higher than normal when too much stabiliser is present in your pool, but this is actually a false reading that is caused by properties of cyanuric acid.

Correcting high CYA levels in a pool will return high total alkalinity readings back to where they were before.

How To Test Your Cyanuric Acid Levels

In order to test the levels of stabiliser or CYA in your pool, you will need an appropriate testing kit. Test kits for cyanuric acid are available in dip-method testing strips as well as testing solutions. We recommend using a CYA testing solution for the most precise results.

If your stabiliser levels are reading above 50ppm, you will need to take steps to lower the CYA in your pool in order to restore the effectiveness of your chlorine and negate the other negative effects of this condition.

How To Lower Cyanuric Acid in Pools

Drain and Refill Method

In order to remove some of the cyanuric acid content from your pool, you can drain some of the water out of your pool and replace it with freshwater. This should only be done in small amounts until a more desirable level of CYA is reached.

You can use this pool cyanuric acid calculator to work out how much water you need to drain and refill based on your pool volume and current CYA level.

If you have an in-ground pool, you should always take extra care when draining any of your pool water. Draining too much water from an aged, in-ground pool can cause pool-popping, a condition where an area of the surface or lining of your pool busts.

This type of pool-popping is caused by a change in the amount of pressure exerted by your pool’s water on the walls of your pool.

Hydrostatic pressure involves a constant application of force against the walls of your pool that is relative to the volume of water that is present. As the volume of this water is decreased through draining, the amount of pressure being exerted on the walls of your pool is also decreased.

Because the integrity of your pool’s lining naturally adapts to withstand the amount of pressure that is exerted on it when your pool is completely full, it can drastically lose structural integrity when this pressure is no longer exerted on it. This is what causes these concrete eruptions known as pool popping.

To avoid pool popping, only drain your water level to a maximum of three inches below the normal water line on your pool before replacing the deficit with fresh water.

If this is not enough to get your CYA within normal range, allow your pump to circulate your water for at least an hour and then perform another water change.

How to Lower Cyanuric Acid In Pool Without Draining

If you are not able to drain and refill your pool easily, you may be able to lower the CYA content of your pool through another method. Certain manufacturers now make products known as bio-active cyanuric acid reducers that can be added to your pool.

These products work by utilising microorganisms that consume and metabolise cyanuric acid at a fairly efficient rate. Although adding microorganisms to your pool may not sound appealing, there is no need to be concerned.

As these microorganisms eat away at the CYA in your pool, your chlorine effectiveness is slowly restored to normal, which in turn kills off these microorganisms and restores your pool to sanitary conditions.

While these sound great in theory, most people who have used them have found that they don’t work very well.

One of the downsides of these CYA reducers is that they need fairly specific conditions to work properly. If these conditions are not met, the whole thing may be a waste of time.

Take note of your product’s listed requirements for water temperature and free chlorine levels.

Although ideal levels for pH and alkalinity are also given, these levels can be hard to manage at this time due to the way high CYA levels affect these readings.

CYA removers can often be added straight to the skimmer box of your pool and are then left to circulate until the treatment is complete. In pools with extremely high levels of stabiliser present, this process can take a maximum of 10 days.

Other pool treatments such as chlorine shock, algaecides, phosphate removers, and clarifiers or flocculants should not be used for at least a week following the introduction of your stabiliser remover.

As mentioned before, these CYA reducers are not highly effective, so draining and refilling is your best option for getting rid of excess cyanuric acid for good.

Preventing High Cyanuric Acid From Reoccurring

High cyanuric acid levels in a pool are caused through two primary methods.

The first one occurs when a new pool owner misunderstands the intended application of CYA, and assumes that using more is better.

The second one occurs when pool owners use an abundance of stabilised chlorine, especially if this product is used as a shock treatment.

When stabilised chlorine is used as a shock treatment and is consumed by neutralising microbes, high amounts of cyanuric acid are left behind.

When using a shock treatment in your pool for any reason, it is important to use unstabilized chlorine to avoid an overabundance of cyanuric acid.

Generally, I recommend using calcium hypochlorite as the chlorine sanitising agent for most pools, because it is unstabilised and you can therefore control the cyanuric acid concentration independently of the chlorine concentration.


Cyanuric acid in your pool above 50 ppm is problematic because it renders your chlorine ineffective.

If you want to lower the CYA level, you need to either partially drain and refill your pool, or use a cyanuric acid reducer.

Draining and refilling is generally recommended because it will permanently get rid of the cyanuric acid, though it is time-consuming.

Cyanuric acid reducers are not recommended because the feedback from many pool owners has been quite poor. Most who have used it say that it has had virtually no effect on their pool.

To prevent this from becoming an issue again, use calcium hypochlorite or sodium hypochlorite (bleach) whenever adding chlorine to your pool.

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.