How to Balance The Cyanuric Acid in Your Pool

Chlorine is important for pool cleaning, but the agent loses its disinfecting effect under the sun’s influence. Is cyanuric acid the solution as a chlorine stabilizer?

Cyanuric acid protects chlorine from UV rays and serves as a chlorine stabilizer in outdoor pools. The cyanuric acid level in the water is measured with a pool tester and should be between 30 – 50 ppm. The chlorine loses its disinfecting effect if the cyanuric acid level is above 50 ppm.

This article will teach you everything about using cyanuric acid in your pool and why the chlorine stabilizer should not be missing in any pool equipment.

How does cyanuric acid work as a chlorine stabilizer in a pool?

Cyanuric acid is a weak acid that acts as a chlorine stabilizer in your pool – it is also known as a pool conditioner or pool stabilizer.

When used in outdoor pools, chlorine has the disadvantage of quickly disappearing down under the influence of UV rays and losing its disinfecting effect in the pool water.

To increase chlorine resistance in your pool, cyanuric acid is used as a chlorine stabilizer.

That is why a chlorine stabilizer is an essential part of chlorine products.

With the chlorine stabilizer, the chlorine in your pool remains effective longer, and less chlorine will be required in the long term.

As a result, it reduces the amount of chlorine used and reduces the cost of pool maintenance.

Chlorine products such as di-chlorine and tri-chlorine already contain a stabilizer. You do not have to use an extra chlorine stabilizer – this is referred to as stabilized chlorine.

But be careful: If the cyanuric acid level rises above 50 ppm, the effect of chlorine diminishes.

This is one of the reasons why the pool water turns green despite using chlorine.

You can easily prevent this by regularly measuring the cyanuric acid level in your pool water with a pool tester and, if necessary, optimizing it – you will find out exactly how this works in the further instructions of the text.

Measuring cyanuric acid in your pool: What is the ideal level?

The proper chlorine dosage combined with a chlorine stabilizer will keep your pool clean and free of algae in the long term.

The requirement for this is that the cyanuric acid level in your pool is between 30 and 50 ppm – the ideal cyanuric acid level is below 50 ppm.

Therefore it is necessary to test the pool parameters ​​at least once a week.

It is best to use the photometric method or the DPD method – a suitable water tester is listed here.

The chlorine stabilizer on most pool test strips is labeled as cyanuric acid and given in ppm. Don’t get confused by the figures in ppm (parts per million) – 1 ppm equals 1 mg/l.

As long as the cyanuric acid does not exceed the limit of 50 ppm, everything is fine.

But what if the limit level of the chlorine stabilizer is exceeded?

The chlorine loses its disinfecting effect with increasing cyanuric acid content, and the impact of chlorine in your pool is completely lost at a certain point.

You would then only pour unnecessarily chlorine into your pool, and no disinfecting effect would be achieved.

In addition, too much cyanuric acid in your pool is considered harmful to health.

The consequences are eye and skin irritation, as the acid is absorbed through the skin when swimming.

However, the problem can be avoided if you dose the chlorine stabilizer correctly and, if necessary, reduce an excessively high proportion of cyanuric acid in your pool water.

In the next chapter, you will learn how to increase and decrease the cyanuric acid level.

How to use cyanuric acid in your pool as a chlorine stabilizer

Measuring the cyanuric acid is only half the job and an essential requirement for the ideal level in your pool.

Correct use of cyanuric acid is critical to avoid overdosing and damaging your expensive pool equipment.

Some advisors recommend pouring the agent into the skimmer or the floater.

But as you’ve learned, the chlorine stabilizer is an acid, and that acid can damage your pool and equipment.

The procedure for using cyanuric acid is as follows:

  1. Take a bucket with a capacity of 20 liters and fill it with water.
  2. Per the manufacturer’s instructions, pour the cyanuric acid into the bucket and stir the mixture with a stick – avoid direct skin contact.
  3. Wait for 10-60 minutes for the remedy to dissolve.
  4. Now pour the dissolved agent over the edge into the basin – done.

The cyanuric acid is better dissolved in the 20 L bucket, and the bucket can also be used later to lower the cyanuric acid level.

You now know how to use cyanuric acid correctly with chlorine in your pool.

In the next chapter, I will explain how you can lower the cyanuric acid level in your pool. Just read on.

How to lower cyanuric acid in your pool

The cyanuric acid level should be below the limit of 50 ppm.

This is important because everything above leads to the disinfecting effect of the chlorine being lost.

The following table clearly shows how the effect of the free chlorine decreases with an increasing proportion of cyanuric acid in your pool water.

Cyanuric Acid Free Chlorine
30 ppm 45 %
50 ppm 30 %
70 ppm 25 %
100 ppm 10 %

If you have measured the pool water and determined that the limit levels ​​for cyanuric acid are too high, it does not help let the pump run longer to break down the acid.

There are also no agents that lower the level of cyanuric acid.

This is because the cyanuric acid does not dissolve in your pool, and the level does not drop even if the water evaporates.

That means: If you use di-chlorine and tri-chlorine – which is already stabilized – the cyanuric acid content in the pool continues to rise, but the chlorine does not have any effect.

And how is a high cyanuric acid level removed?

Well, you may think that the swimming pool flocculant could help, but that is not the case with cyanuric acid.

Only one thing helps lower the cyanuric acid level in your pool: Drain the pool water.

But how much water has to be skimmed off or drained from your pool to achieve the ideal level?

Let us assume that the cyanuric acid has a level of 100 ppm, and the level should be reduced to 50 ppm. That means you have to replace 50% of your pool water.

Later, the pool is regularly rinsed and topped up with fresh water to keep the ideal cyanuric acid level in your swimming pool.

How to raise cyanuric acid in your pool

The cyanuric acid level would be too low, below 30 ppm. In this case, you have to raise the cyanuric acid.

This is because chlorine quickly loses its effectiveness due to the sun’s UV rays.

In the case of di-chlorine and tri-chlorine, the problem of a low cyanuric acid level will generally not be encountered since these chlorine products are already stabilized and can be used without an additional chlorine stabilizer.

To be on the safe side, always measure the levels ​​in your pool water once a week and, if necessary, lower the proportion of cyanuric acid.

Suppose the cyanuric acid level in your pool is too low. In that case, follow the manufacturer’s instructions to increase the cyanuric acid level, as each agent is dosed differently.

Suitable cyanuric acid for pool maintenance – which you can buy online – is listed in the article.

When should cyanuric acid be used in a pool?

Cyanuric acid should always be used when using non-stabilized chlorine – this often includes granular chlorine and liquid chlorine.

It is best to use cyanuric acid immediately after using the chlorine in your pool.

But you can already buy stabilized chlorine granulate (di-chlorine or tri-chlorine) – pay attention to the product description – then you don’t have to use extra cyanuric acid.

Liquid chlorine usually does not contain a chlorine stabilizer because it is used for pool shock.

This means: Liquid chlorine that has already been stabilized is suitable for long-term disinfection in your pool, but not for a pool shock because the stabilizer it contains slows down the effect, and there is no shock.

You can read everything you want to know about the pool shock in my blog. There is also a guide on how to apply a pool shock.

Other occasions when you should use a chlorine stabilizer are cloudiness in your pool.

If the cyanuric acid level is too high, the effects of chlorine are suspended, and your pool water becomes cloudy.

The water in the pool must be clear, and if you notice cloudiness, you should possibly measure the acid capacity.

Note: Basically, a stabilizer is always applied to the chlorine to work longer. Free chlorine in the water is particularly important when you clean your pool.

When is a chlorine stabilizer in your swimming pool useless?

In an outdoor pool, a chlorine stabilizer should always be used in addition to the free chlorine, as the UV radiation from the sun harms the effectiveness of the chlorine.

You don’t need an additional chlorine stabilizer if you use di-chlorine or tri-chlorine in your outdoor pool because these already contain a stabilizer.

Since the UV radiation is only feeble in an indoor pool, you do not need cyanuric acid in this case.

Furthermore, no cyanuric acid is necessary when using Bromine for disinfection, as Bromine is not sensitive to UV rays. Source.

But avoid using the chlorine stabilizer in your whirlpool (spa).

In the whirlpool, it is essential to kill pathogens with the chlorine immediately, and the chlorine stabilizer would only cause this process to take 100 times longer.

I recommend using hydrogen-oxygen instead of chlorine in a hot tub.

Whirlpools are usually in a closed room or are covered, which eliminates the need for a stabilizer.

Of course, you don’t need cyanuric acid if your pool is operated without chlorine.

Do you have further questions about the chlorine stabilizer?

Use the search function or contact me at @contactswimfool on Twitter, Facebook, or YouTube with your question – I’ll be happy to help.

With that in mind, have fun in the pool.

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Hi. I'm Max Berg. I've been in the pool industry since 2015 and have always felt drawn to water. I'm the author behind swimfool.com, where I share my years of experience in pool maintenance and give helpful tips on keeping a swimming pool or hot tub clean. My tips reduce the costs of water treatment and protect the environment.

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