Poor water quality in the pool cannot always be remedied by simple cleaning measures. In some cases, shock chlorination is necessary. In this article you will learn what shock chlorination is.

In a nutshell

  • Shock chlorination improves bad water parameters
  • high levels of chlorine are added to the water
  • Chlorine level rises sharply
  • Effect: thorough cleaning of the pool water

Shock chlorination explained

Shock chlorination is the opposite of permanent chlorination. While the pool stays clean for a long time with continuous chlorination, shock chlorination is only used when the water is no longer ideal or has already tilted. The measure is an emergency solution to compensate for poor water values and in this way make the water in the pool suitable for bathing again. For this purpose, the water in the pool is "shocked" by the addition of large amounts of chlorine. This means that the amount of chlorine increases so much over a short period of time that there is enough free chlorine to stabilize the water values:

  • Baseline less than 0.5 parts per million (ppm)
  • often initial values below 0.02 ppm (tipped water)
  • Target value of over 4 ppm
  • The chlorine value then drops
  • Pool can be walked on again afterwards

Notice: It is important that you clean the pool prior to chlorination. This is the only way the chlorine can work, since the substance only helps to a small extent against existing dirt.

Shock chlorination: when necessary?

As already explained in the previous section, the shock chlorination should optimize the water parameters within a short time. But when is it necessary? There are several signs that indicate this and that you should not ignore. These include:

  • clearly visible opacities
  • unpleasant smells
  • low chlorine values after measurement

However, such problems can not only occur due to a lack of cleaning measures or a missed permanent chlorination. The following reasons can quickly change the water quality, making shock chlorination necessary:

  • intense heat exposure
  • large amounts of dirt from storms
  • more bathers than usual
  • Food or drink in the pool
  • faeces

Shock chlorination: dosage

In order for shock chlorination to be successful, the dosage must be right. While you need between 1.5 and two grams per cubic meter of water for continuous chlorination, the value for shock chlorination is significantly higher. You have to reckon with 10 to 15 grams per cubic meter put into the water. If the water is completely dumped, you will probably need to use more if the amount mentioned is not enough.

Suitable chlorine variants

Chlorine granules are used for chlorination, since classic tablets are not suitable for this purpose. In addition, the chlorine granulate is much easier to dose, which makes it all the more effective. There are three different types of chlorine available to you, which depending on their composition may or may not need to be dissolved in water before use:

  • Calcium hypochlorite (65 percent chlorine): pre-dissolve
  • Dichlor (60 percent chlorine): do not pre-dissolve
  • Lithium hypochlorite (35 percent chlorine): do not pre-dissolve

Notice: It is important to wear suitable protective clothing during the measure. These include safety goggles and gloves, so that your skin and mucous membranes do not come into contact with the chlorine.

frequently asked Questions

When is the best time to perform chlorination?

The chlorine achieves the best effect if you carry out the measure at dusk or at night with water temperatures of 15°C to 18°C. If the sun acts on the fabric, it will break down and the chlorination will not work.

How long should you not bathe after shock chlorination?

If you are wondering when you can swim again after the measure, you don't have to wait that long. The water must have a maximum of 3 ppm chlorine. Higher levels of chlorine are harmful to the skin and mucous membranes. In most cases, this value is reached eight hours after chlorination, but waiting times of more than 48 hours are not uncommon.

What pH should the water for shock chlorination have?

You must not use the intensive chlorination if the water has the wrong pH value. This reduces the effect of the chlorine. The water must have a pH of 7.2 for the chlorination to work. If this value is not available, you need to lower the alkalinity of the water.

Can the measure be carried out without chlorine?

Yes, potassium peroxomonosulphate is used for this. This substance is a potassium compound, which is also offered under the name oxygen granules. The alternative enables good water values after a waiting period of around 15 minutes, after which you can immediately use the pool again. But you have to be prepared for a significantly higher purchase price.

Why is backwashing important during chlorination?

If a shock chlorination is carried out, a lot of dirt accumulates in the filter system. For this reason, you must remove all residues from the filter before chlorination, so that it does not become clogged. It is also important to carry out the backwash after chlorination so that there are no residues in the water.

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Garden design