Chlorine Guide: What Types of Chlorine are Used For Pools?

The use of chlorine is important for keeping the water in your pool clean. But what is the difference between the individual types of chlorine used for pool maintenance?

When measuring the chlorine level in the pool, a distinction is made between free, bound, and total chlorine. A difference must be made between stabilized and non-stabilized chlorine when using it. Common types of chlorine are granulated chlorine, liquid chlorine, and chlorine tablets.

This comprehensive guide will provide a detailed explanation of chlorine in your pool and how the different types of chlorine can be optimally used for pool maintenance.

Difference between free, combined, and total chlorine

Before I explain the individual types of pool chlorine in more detail, you should learn what the terms free, combined, and total chlorine in your pool water mean.

Because it primarily does not matter which chlorine is used for disinfection. The chlorine in your pool is always measured according to the same principle.

You can find the proportion of chlorine in your pool and the differences in the measured levels in this table.

Chlorine Difference Outdoor Pool Indoor Pool
Free Chlorine Actually available chlorine for disinfection 0,4 ppm 0,8 ppm
Bound Chlorine Reaction of chlorine with ammonia and other ammonium compounds 0,2 ppm 0,2 ppm
Total Chlorine Sum of free and bound chlorine 0,3 – 1,5 ppm 0,3 – 1,5 ppm

The optimal amount of chlorine in pool water is determined according to DIN 19643 – The DIN standard states that the difference between free and bound chlorine should not be more than 0.6 ppm.

An example: If the proportion of free chlorine is 0.8 ppm and the combined chlorine is 0.2 ppm, then the limit (difference) of 0.6 ppm is not exceeded.

An electric water tester can precisely measure the chlorine level in your pool.

But how much chlorine is ideally used in pool water?

When using chlorine, always follow the manufacturer’s dosage instructions, then you will not have a problem with too much chlorine in your pool water – you can read more about the topic in my blog under the link.

But that doesn’t apply to a pool shock – In this case, a short-term overdose of chlorine in your pool is desirable.

In the next chapter, you will find out which type of chlorine you can use for shock chlorination and when another chlorine would be the better choice.

Difference between stabilized and non-stabilized chlorine

Chlorine is available as chlorine granulate, liquid chlorine, or chlorine tablets for your pool maintenance.

These types of chlorine are also differentiated between stabilized and non-stabilized chlorine.

Use of stabilized chlorine in swimming pools

Stabilized chlorine is mixed with cyanuric acid (chlorine stabilizer) and, in this way, protected from rapid decomposition by the sun’s UV rays.

What’s the difference between di-chlorine and tri-chlorine:

  • Di-Chlorine: Sodium dichloroisocyanurate dissolves more quickly in water than tri-chlorine.
  • Tri-Chlorine: Trichloroisocyanuric acid is cheaper than di-chlorine, but dissolves more slowly.

Both types are organic chlorine products and, thanks to the cyanuric acid, build up a high level of chlorine in your pool.

That means: With the Di-Chlorine and Tri-Chlorine, you can disinfect your pool water continuously.

You need about 400 g/week of tri-chlorine in the high season – around 10 to 12 kg of chlorine are necessary for pool maintenance each year.

The chlorine granulate is also helpful to get rid of local infestation by green algae. To do this, the granules are applied to the affected areas.

In my blog article on cleaning green pool water, I go into more detail on the topic.

You should know that di-chlorine and tri-chlorine are unsuitable for a chlorine shock in your pool.

This fact is because of the chlorine stabilizer it contains, which prevents rapid disinfection.

Highly concentrated chlorine products without a chlorine stabilizer are required for a pool shock. You can find out more in the following chapter.

When do you use non-stabilized chlorine in your pool?

Non-stabilized chlorine does not contain a chlorine stabilizer (cyanuric acid), and therefore this type of chlorine is wonderfully suitable for a pool shock.

The non-stabilized chlorine is often offered in liquid form in pool shops.

But be careful: There are also liquid chlorine products that contain cyanuric acid – I recommend the following product.

If you use non-stabilized chlorine, then the overdose of chlorine in your swimming pool is intended to remove the cloudiness.

The non-stabilized chlorine is available in different concentrations, and the amount used for the pool shock is adjusted depending on the concentration.

In the technical article, you can learn how to perform a pool shock chlorination.

Tip: A non-stabilized chlorine is used for the permanent disinfection of your pool water with the help of cyanuric acid. You can use the search function on my blog to find more information about cyanuric acid.

Chlorine types and their differences

Chlorine is one of the most effective disinfectants for treating pool water.

The use of chlorine in a pool is effective in:

  • Cloudy pool water: Cloudiness in the water due to organic pollution is eliminated.
  • Legionella: The dangerous legionnaire’s disease is eliminated with chlorine.
  • Germs and bacteria: All kinds of germs and especially against E. Coli (Escherichia Coli).
  • Algae: The natural growth of algae in the pool is inhibited.

But not all chlorine is suitable for fixing cloudy pool water or black algae.

Each chlorine is intended for a special application in your pool and must therefore be used correctly.

The chlorine (CL) is offered in different forms, which confuses many beginners.

The difference between the individual types of chlorine is illustrated in the following table.

Chlorine Description Application
Stabilisiertes Chlor A chlorine that is mixed with cyanuric acid (chlorine stabilizer) Suitable for permanent disinfection in the pool
Di-Chlorine Sodium dichloroisocyanurate is a stabilized chlorine and dissolves quickly Suitable for permanent disinfection in the pool
Tri-Chlorine Already stabilized trichloroisocyanuric acid, which is cheaper than di-chlorine Suitable for permanent disinfection in the pool
Calcium Hypochlorite It is available as granules, and it is not stabilized Suitable as a pool shock and for permanent disinfection
liquid Chlorine Usually, non-stabilized chlorine in liquid form Suitable for chlorine shock
Chlorine Tablets For the production of free chlorine in water Use via a floater or in a skimmer
Chlorine Gas Increased security measures and systems are necessary The gas is not used in private pools

In addition, the differences in chlorine mentioned in the table are explained in detail again.

Chlorine granules (calcium hypochlorite) in the pool water

The chlorine granulate – calcium hypochlorite – is relatively cheap and is most often used in private swimming pools to disinfect the water.

The reason for this is that the chlorine granulate can be used to increase the chlorine content in the pool quickly and permanently in order to prevent cloudiness.

Calcium hypochlorite is commercially available as a fine powder or as granules.

Attention: When buying, I should note that the calcium hypochlorite is offered as stabilized and non-stabilized chlorine.

If you want to shock your pool with calcium hypochlorite, use non-stabilized chlorine granules.

The stabilized calcium hypochlorite is used for permanent disinfection of your swimming pool water.

Liquid chlorine products for pool maintenance

Liquid chlorine (sodium hypochlorite) usually does not contain a chlorine stabilizer and is often used for a pool shock.

But the liquid chlorine can also be used for permanent disinfection in the pool. For this, you have to stabilize the chlorine with cyanuric acid.

When using it, the liquid chlorine is poured undiluted into your pool.

When using liquid chlorine, splashes often occur, and bleach stains appear on the affected areas at your pool – it is best to wear old clothes.

Furthermore, chlorine is a dangerous good, and you should therefore always wear protective equipment (mask and glasses).

Tip: If the calcium content in your pool is above the ideal level, then liquid chlorine is preferable to chlorine granulate. This is because the granules increase the calcium content in your swimming pool.

Use of chlorine tablets in the pool

In addition to using chlorine granulate and liquid chlorine, the chlorine tablets are practical to continuously produce free chlorine in your pool.

At the top of the article, I explained that free chlorine is necessary for disinfecting the pool water.

That’s why I would always recommend using a chlorine tablet for your pool maintenance.

The chlorine tablets are ideally dissolved in the water using a floater.

The skimmer can also be used as an emergency solution, although the floater is the better choice.

The problem with using chlorine tablets with a floater is the dosage.

And when the tablets are placed in the skimmer, 20% of the effect is lost. This leads to increased costs for disinfecting the pool water.

Tip: It is not uncommon for beginners to find that there is too much chlorine in their pool due to chlorine tablets. I recommend a chlorine metering sluice to avoid an overdose of chlorine in your pool.

Use of chlorine gas in swimming pools

The chlorine gas is usually not used in private swimming pools because it must be delivered in large containers and would be too expensive for private consumers.

The use of chlorine gas also increases the risk of accidents and necessary increased safety precautions.

But there is another alternative to disinfecting the pool, which should not go unmentioned.

But the types mentioned above of chlorine are sufficient for the domestic pool, and you clean your pool without the chlorine gas.

Is it dangerous to use chlorine in the pool?

The chlorine is effective in keeping pool water clean at a low cost.

But is it dangerous to use chlorine in your pool?

One thing must be clear: Chlorine (CL) is a poisonous chemical and should therefore be avoided by direct skin contact and inhalation of the gases when used in a pool or hot tub.

The use of chlorine in your pool is questionable, as dangerous by-products such as trihalomethane (THM) and chloramines are formed. Source.

  • Trihalomethane: If chlorine in your pool water reacts with organic substances, trihalomethane is formed. Studies have shown that a high concentration was gold-plated as carcinogenic.
  • Chloramine: When chlorine reacts with sweat and urea, chloramines are always formed. This chlorine by-product is noticeable in the typical indoor pool smell and eye irritation.

But, dissolved in the water and correctly dosed, the chlorine in your pool is harmless. Just make sure that the chloramines and trihalomethane do not rise above 0.2 ppm.

Stick to the use of chlorine and carry out a water test regularly, then the use of chlorine is relatively safe.

If the level of chloramine and trihalomethane is above the limit of 0.2 ppm, you can lower the level by just adding fresh water into your pool.

I should mention that side effects can occur despite the correct use of chlorine in your pool or hot tub.

An allergy or, in the worst case, chloracne is not uncommon.

Therefore, always wear appropriate protective equipment before working with chlorine.

Alternatively, you can wear sunglasses and a scarf to protect yourself halfway. However, this is not a replacement for proper protective equipment.

Tip: Inhaling the chlorine gases can be prevented by opening the container with chlorine quickly and at the same time moving away until the gases have disappeared.

FAQ about using chlorine in a pool

In this chapter, you will find other interesting questions about chlorine.

Is every single chlorine the same?

A difference is made between stabilized and non-stabilized chlorine. The difference between free, bound, and total chlorine content is also essential.

Only bound chloride is found in nature.

The chloride is not to be confused with the industrially produced chlorine.

What is the difference between chlorine tablets and chlorine granules?

The chlorine tablets are used to continuously generate free chlorine in your pool water – This is the main chlorine for disinfecting the pool or hot tub.

At the same time, the chlorine granulate is suitable for general disinfection and also for a pool shock.

What is the difference between chlorine and active oxygen?

Chlorine is cheaper than active oxygen (hydrogen peroxide), whereby chlorine creates disinfection by-products such as chloramines and trihalomethane.

The consequences of an incorrect dose of chlorine are eye irritation and the typical indoor pool smell.

The use of active oxygen in your pool, on the other hand, is considered harmless and is much more pleasant for bathers.

How can you measure the proportion of total chlorine?

Electronic water testers are best for determining the exact amount of chlorine in your pool water.

The proportion of total chlorine results from the sum of free and bound chlorine – ideally, the chlorine level is below 1.5 ppm.

What to do if the free chlorine is too high?

A freshwater supply can lower the chlorine level if you have too much free chlorine in your pool water.

Please note, however, that the pH level may have to be optimized by adding fresh water.

What to do if the free chlorine in your pool is too low?

By using chlorine tablets in a floater, you can continuously produce free chlorine and increase the amount of free chlorine.

If you use a lot of chlorine in the pool and the free chlorine is still too low, then the pH value and the total alkalinity may not be optimal.

How to lower the combined chlorine in my pool?

The combined chlorine still has a disinfecting effect but is not as strong as the free chlorine.

Here, too, a partial water change can help to lower the bound chlorine.

Which is better, chlorine or multi-tabs?

Pure chlorine is much more effective in treating pool water.

The multi-tabs are practical, but you should not use multi-tabs for professional pool cleaning.

Which is better, chlorine granulate or liquid chlorine?

Both means, chlorine granulate and liquid chlorine, are suitable for maintaining the pool.

The liquid chlorine can be poured directly into your pool water for a pool shock treatment, while the water bucket granules must be dissolved.

Whether you use chlorine granulate or, liquid chlorine depends on the application. I recommend having both remedies in stock.

Have you any further questions about the chlorine types used for pool maintenance?

Ask me @contactswimfool on Twitter or Facebook.

Have fun using chlorine, and stay safe!

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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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