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In order to be able to bathe in clean, clear water for a long time, the right chlorine value in your pool is essential. It ensures that pathogens or algae cannot spread.

In a nutshell

  • Measure chlorine level via tests
  • Chlorine levels should be neither higher nor lower than recommended
  • if there is too much chlorine, changing the water will help
  • add chlorine if the values are too low

What chlorine is good for

Most people are familiar with the typical smell of chlorine in a swimming pool. However, many do not particularly like the idea that the home garden pool smells similar, since the chemicals are avoided. However, chlorine is very important in the pool. Filtering alone cannot keep many substances out of the water that would adversely affect the water quality in the long run. These include fungi, viruses, bacteria and, above all, algae. Chlorine reliably eliminates all of these substances in the water. In order for this to be successful in the long term and for the water to remain stable, the chlorine value in the pool must be set correctly.

The perfect chlorine level

The chlorine level in the pool should be between 0.3 and 0.6 mg/l. With these values, the water stays clean and the chlorine does not harm. However, the value fluctuates constantly. Responsible for this are:

  • usage (how often, how many people, how long)
  • Rain, water changes or dirt
  • Filter systems or other running devices
  • Sun exposure (UV light breaks down chlorine and promotes algae growth)
  • fluctuating pH values

How the chlorine content is determined

There are various test options to correctly determine the chlorine level in the pool. It is important to use the same method whenever possible so that the values are comparable. Testing is done when the pool is refilled, then at regular intervals until the perfect chlorine level is set and stable. A weekly test is then sufficient.


There are test kits that are not only suitable for the chlorine level in the pool, but also for the pH level. Kits include tablets that dissolve in water and produce a color reaction.

test strips

Test strips have been around for a long time and they are also comparatively cheap. Depending on the provider, other water values can also be read with the test strips. The application is very simple. The test tire is briefly immersed in the water and the chlorine value in the pool is then read off the associated scale.

drop tests

Drop tests for measuring pH are relatively easy to use and provide more accurate results. If you can't find them in pool accessories, you can also find them in aquarium accessories. The water to be tested is filled into a glass cuvette, the necessary drops of the test liquid are added according to the instructions on the package and the water changes color.

Notice: For all tests, only use the scale provided on the packaging for reading, otherwise the values are unreliable.

Digital Measurements/Electronic Gauges

There are various ways in which the devices measure the chlorine level in the pool and sometimes also the pH value. The operating instructions provide information on how to use the device. More expensive devices can display more than just chlorine and pH. However, most of the other water parameters are irrelevant for the pool. The situation is different if there is also a freshwater aquarium or a pond in the household. A test device can then be used to determine all the necessary parameters so that humans and animals remain healthy.

Increase chlorine level

If the measured value is too low, chlorine is added until the perfect chlorine value is reached in the pool. The chlorine is used in the form of tablets or granules. However, it should not be added directly to the pool. It is better to dissolve the chlorine in a little water beforehand and then slowly add it to the pool with the filter switched on.

Reduce chlorine level

Too high a chlorine value in the pool can not only affect your own well-being while bathing. It will also cause the pool liner to fade or may corrode the material of some accessories. The easiest and quickest way to reduce the value is to do a partial water change. Either no chlorine is added to the new water or only a little.
If the level does not need to be reduced immediately, swimming can be delayed until the chlorine level has gone down on its own. This happens quite quickly, especially in direct sunlight.

Notice: If a dosing system for chlorine is installed, it should be checked whether this is responsible for the excessively high chlorine value. It may need to be reset.

Changing chlorine levels in the pool

If testing reveals that the chlorine levels in the pool are constantly changing, the next step should be to check the pH. If this value is not set correctly, the chlorine value cannot stabilize. The pH should be around 7.2. Appropriate substances that reduce or increase the pH are suitable for adjusting the pH value. They are added to pool water according to package directions.

frequently asked Questions

What is shock chlorination?

Shock or shock chlorination involves adding much more chlorine than normal. This fights major problems in the water or prevents them from occurring. This includes, for example, a green discoloration of the water due to an algal bloom.

Is chlorine harmful?

Diluted in the right concentration in the pool water, it does not harm the skin or mucous membranes. However, pure chlorine is corrosive, even if inhaled, so care should be taken when chlorinating. Protective clothing is mandatory.

Can a pool be operated without chlorine?

It's theoretically possible, but not advisable. The easiest way to keep a pool clean without chemicals is to change the water frequently. However, this is associated with high water consumption. Some other (also chemical) substances are recommended as an alternative to chlorine, including, for example, bromine or active oxygen. A UV system reliably kills bacteria, viruses or fungi.

Which chlorine supplements are best?

That depends on usage. Granules dissolve quickly, tablets are better used in a dosing system. The easiest way to use liquid chlorine is in the pool.

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