How to Shock a Pool With Bleach

By Greg Jarvis | Last Updated: September 8, 2022

Is it necessary to shock a pool with bleach? The answer is yes. The purpose of shocking a pool with bleach is to boost the concentration of free chlorine. You can do this using a commercial product, which works well on freeing the chlorine that has produced compounds with contaminants.

Adding more chlorine and bleach into the pool can be done as well. Make sure that the pH is in the appropriate range, generally between 7.2 and 7.8, and then pour the bleach in the evening to prevent degradation by sunlight.

When Should Shocking Be Done?

Green or cloudy pool water is an indication that the level of free available chlorine in the swimming pool is quite low to provide the appropriate sanitation. If you test the water, you will find out that the level of free available chlorine has reduced and does not meet the allowable value of 1 part per million.

This is despite the fact that the concentration of chlorine still meets the standard limit. This usually happens when chlorine has formed compounds known as chloramines along with bacteria and other elements and is not available for sanitizing. The compound chloramines produce a distinct odor of chlorine, even if the concentration of the chemical is low.

Why Use Bleach as a Shock?

Most of the commercial pool shock has chlorine, but most of the time, it contains other chemicals as a replacement for chlorine in the compounds and makes it available for sanitizing. A minimal amount of this product should be used as compared to when using chlorine, and if you prefer chlorine alone, more bleach is required than you do pool chlorine.

The main component of bleach is sodium hypochlorite and is used as pool chlorine. However, the concentrations are different. The sodium hypochlorite concentration in pool chlorine is between 10% and 15%, while in bleach, it is only 5% and 6%.

It only means that you require twice as much bleach as the pool chlorine and since the main objective of shocking is to increase the free chlorine concentration to 5 to 10 ppm, that could add up to a lot of bleach.

Another essential thing to consider is that chlorine easily degrades in sunlight. Usually, the pool contains cyanuric acid at high concentrations. This chemical stabilizes chlorine, to avoid degradation, and if it does not, you can add more.

The recommended time of adding the bleach is in the evening or in the late afternoon. This will allow the chemicals to work for some time in the dark. Even if the cyanuric acid concentration is within the acceptable limit, you can still add more bleach.

How to Shock the Pool Using a Bleach

Here are the simple steps on how to do it:

Step#1 – Testing the Pool Water pH

Knowing the pool water pH is the first thing you need to do. If it is too high, add sodium bisulfate or muriatic acid to lower it. Chlorine easily loses its effectiveness if the pH level is above 7.8. The water pH should be between 7.2 and 7.8.

Step#2 Check the Cyanuric Acid Level

In checking the Cyanuric acid level in the pool, you need a special test kit. The result should be between 20 and 50 ppm. In case the result is too low, you can add a stabilizer to increase the concentration. Check the stabilizer container and carefully follow the instructions on how to use the product.

Step#3 Determine the Amount of Bleach Needed

Measure the volume of water in your pool to help you determine the amount of bleach needed. Follow the formula:

  • Pool width x pool length x average depth of water = water volume

Then calculate the volume of bleach required based on this – 1 gallon will increase the free chlorine level of 30,000 gallons of water by 2ppm. In case you need to mildly shock a 30,000 gallon of water to raise the free chlorine concentration to 5 ppm, you need to add at least 2.5 gallons of bleach. If you need to raise it to 10 ppm, add 5 gallons of bleach.

Before you go next step you can read more about the best pool chlorine tablet.

Step#4 Add the Bleach

As mentioned earlier, it is best to add bleach in the late afternoon or early evening. In pouring the bleach, start at the edge of the pool and then walk around the perimeter. Make sure not to pour it into the skimmer. After adding the bleach, circulate the water for several hours. This will ensure that you have thoroughly mixed the bleach in the water.

Make sure you have followed the steps carefully to avoid overdoing the process.

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