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When the pool water turns green, bathing is no longer fun. It's time for a shock chlorination to combat green pool water. You can read here what to look out for and how it works.

In a nutshell

  • the pool water turns green when the water values are no longer correct
  • testing is essential before chlorine is added
  • certain pH values must be observed for clear water
  • Carry out shock chlorination regularly

Cause of green pool water

Pool water turns green when there are so many nutrients in it that algae grow excessively. Algae are in almost every water because they only exist in spores and it is almost impossible to get rid of them completely. Keeping algae counts below a visible limit is achievable with proper pool maintenance. This also includes shock chlorination, which is used in particular when the pool water is already green or cloudy.

Other reasons for carrying out a shock chlorination:

  • major changes in or around the pool that could result in contamination
  • For pools with water level at ground level: Wild animals have fallen into or bathed in the pool
  • very many users in a short time (pool party)
  • very high temperatures or rapid changes in temperature
  • heavy rainfall, especially during thunderstorms

What is shock chlorination?

To keep the pool water clear, a little chlorine is always added to the water. It suppresses microorganisms and eliminates bacteria. However, with shock chlorination, the amount of chlorine is increased to make the chlorination more effective.
preparations containing chlorine

To “shock” the pool, means are used that release chlorine in the water. The higher the chlorine content in the selected agent, the less of it has to be added to the water. In addition, the agents differ in their solubility. If it is tabs or granules, they should be pre-dissolved before they are put into the pool water so that the chlorine is distributed more evenly.

Notice: Tabs can also be placed whole in different places in the pool so that the chlorine is better distributed.

Test pool water

Before shock chlorination can be carried out on green pool water, some water parameters in the pool must be determined. These include the pH value, the chlorine value and the temperature. There are different methods of testing water. The easiest way to measure temperature is to use an ordinary thermometer. The pH value can be determined with test strips. There are also test sets that measure pH and chlorine levels simultaneously.

Check pH

Before you start, these water values should be ensured:

  • pH: between 7.2 and 7.6
  • Temperature 15 to 18 degrees
  • Chlorine content below 3%

Notice: If the pH value is too high or too low, it can be adjusted correctly by adding a suitable dose of fresh water or appropriate preparations.

In addition, the necessary amount of chlorine for the treatment must be calculated. Instructions are usually printed on the respective packaging.

Necessary equipment:

  • Protective clothing, including eye protection and gloves
  • large, clean bucket (20 liters, best used solely for chlorination)
  • long wooden stick for stirring

Instructions for shock chlorination

To ensure that the chlorine is not broken down too early by UV light, the shock chlorination in the green pool water is best carried out in the evening or at least on a cloudy day.

  1. First the Thoroughly clean the pool and remove coarse dirt.
  2. The Also clean the filters and then switch on.
  3. put on protective clothing.
  4. Pour 15 liters of water into the bucket, the calculated one add chlorine and stir with the stick until it has dissolved.
  5. The finished Pour the solution carefully into the pool, preferably near the filter inlet or while walking along the edge of the pool.
  6. The Measure chlorine level. It should now be around 3%. If not already, redissolve a smaller amount of chlorine and add until the correct level is reached.
  7. As long as the chlorine level is that high, it is Pool not suitable for swimming. So keep children and animals away! As a rule, the chlorine has sufficiently degraded after about 8 hours.

Notice: Chlorine bleaches very strongly, which is why it makes more sense to only wear old clothes.

Subsequent algae control & prevention

Depending on whether the selected preparation already contains an algaecide or not, the pool water can still be green even after chlorination. Then the anti-algae agent is used afterwards. So that the pool water does not turn green again so quickly, a few things should be observed:

  • as little sun exposure as possible
  • use nutrient-poor water
  • Maintain filters regularly
  • Chlorine or otherwise disinfect water regularly
  • Avoid nutrient input and pollution

frequently asked Questions

What to do if the water is cloudy after chlorination?

The filter should remain on during chlorination. If the water still remains cloudy, you can try whether a filter backwash brings improvement. Flocculants can also help to dissolve turbidity in the water.

How dangerous is shock chlorination?

Chlorine can be dangerous, not only when it comes into contact with the skin, but also when the fumes are inhaled. It irritates the mucous membranes and lungs. Therefore, protective clothing is strongly recommended. It is best to only handle chlorine outdoors. Chlorine poisoning can have serious consequences.

How often should shock chlorination be performed?

As a rule, shock chlorination should be carried out about every two weeks. Under certain conditions, it can also occur more often. In summer, with high temperatures, it is recommended every week.

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