How to Shock A Pool

How to Shock A swimming Pool

In this article, I will cover step-by-step how to Shock a Pool the Right Way, in just a few simple steps!

What Exactly Is A Pool Shock?

Pool shocking means hyper-chlorinating the water in order to kill bacteria and other organic entities that are present in it. Shocking helps to keep pool water safe for swimmers and is an integral part of regular pool maintenance.

Why Does Pool Water Need to be Shocked?

When chlorine disinfectants in the pool react with sweat, oils and urine (gross yeah? I know), they form chloramines. Shocking helps to negate chloramines and also helps to prevent build-up of algae in the water.

Note that Sunshine causes chlorine levels in the pool to fall by up to 5 ppm (parts per million) in a single day. People who swim in the pool constantly introduce bacteria and other contaminants into the water. Rain causes pool water to become diluted and consequently, it becomes conducive to the growth of algae and bacteria.

While shocking, chlorine levels are temporarily raised to 3-5 times above normal; this kills off everything that has no place in the pool and increases the availability of effective chlorine (Free Chlorine).

When/How Often Should You Shock Your Swimming Pool?

Cloudy Swimming Pool Water

Pool water needs to be shocked on a fairly regular basis depending upon usage and temperature. It is recommended that you shock the pool at least once every month and at the beginning of every season.

If you are seeing signs of algae and/or if the pool water is looking cloudy, this is a sure-shot sign that the pool needs to be shocked immediately.

Commercially available chlorine testing kits help to determine the levels of chlorine in the water. If free chlorine levels fall below 3 ppm, it is time to shock the pool.

Here is a quick lesson on chlorine levels:

  • Effective chlorine or free chlorine: This is the amount of chlorine that is available for use. In other words, it is free to do its job. It has not combined with other substance.
  • Combined chlorine: This type of chlorine has already been used for killing germs and bacteria (to form chloramines). So yes, even though it is still present in the water, it is not really useful. If levels of combined chlorine are high, it means that there is less free chlorine available to kill germs.
  • Total Chlorine: This is simply the sum of free and combined chlorine. Note that even though total chlorine levels may be high, it does not mean that the pool water is sanitized.

Pool Shock – Instructions:

Now that you’ve learnt about what is shocking and why it is essential, let's get down to the actual business of executing a pool shock.

We have already discussed that the Sun causes chlorine levels to plummet. Hence, shocking is best performed at night or in the evening, after the Sun has gone down.

While there are many shocking kits available in the market, I recommend that you shock your pool with Calcium Hypochlorite. It delivers a powerful shock and neutralizes germs that are capable of causing diarrhea and ear, skin and wound infections.

All instructions and amounts are available on the packet. Follow them to the dot.

Irrespective of which product you choose, protect your skin and eyes by wearing eye-glasses and gloves. You will need to determine the amount of chemical needed as per the size of your pool.

Calcium Hypochlorite usually comes in granular form and more often than not, it needs to be dissolved in a pail of water before adding to the water.

  • Once you’ve mixed/prepared the chemicals in the right amounts, you need to introduce them into the pool. 
  • Depending upon the product that you’ve chosen, the manufacturer may recommend pouring it in various areas of the pool or near the jets so that it gets circulated quickly.
  • Once poured, it is advisable to let the chemistry perform its magic for a period of at least 8 hours.
  • Many people leave it overnight.
  • Please refer to the manufacturer’s instruction if in doubt. It is extremely crucial that nobody enters the pool when it is in the process of being shocked.

Important Note: Your pool’s pH needs to be properly balanced when shocking. Ideal pH levels range between 7.2 to 7.6. If the pH is more than 8, the shock won’t be as effective and you’re just wasting your time, energy and money.

See Related Blog Posts:

  1. How to Lower PH In Pool
  2. How to Raise PH In Pool

Shocking kills bacteria and algae but it does not remove them from the pool. Hence, in order to get rid of the debris, run you pool’s filtration system for at least 8 hours or preferably, for one whole day.

Check the pool chemistry for various parameters like chlorine levels, pH, alkalinity and ensure that they’ve returned to normal. Now your pool can be enjoyed to your heart’s content.

Important things to consider regarding pool shock:

Chlorine shock usually renders the pool unusable for several hours. If the pool is being heavily used and needs to be shocked quickly, you may opt for a potassium peroxymonosulfate shock (non-chlorine). This type of shock usually takes just a few minutes and then, the pool is ready to dive into. Non-chlorine shock is often used for vinyl pools and as a quick way to kills germs in-between ‘proper’ shocking sessions.

Just as it is essential to shock a pool at the start of the season, it should be shocked before winter too. Algae spores may be present in the water and you certainly don’t want them to continue infesting the pool over the next 6 months. Algae can be extremely hard to get rid of and can damage pool equipment.

Pro tip: An easy way to sanitize pool cleaning equipment is to throw it into the shallow end of the pool while shocking.

Be wary of shocking on windy and rainy days. Also, check water chemistry after rainy/stormy conditions. It might have been altered radically even if you’d shocked the pool recently. Wind and rain bring in a host of algae spores and in the right environment, they begin to bloom within a matter of hours.

Invest in a good pool cleaning robot. It plays a massive role in keeping the pool clean and well maintained. An automatic pool cleaner is way more affordable than pool cleaning contracts and comes loaded with features such as cleaning cycle scheduler, remote control for spot cleaning, filter full indicator etc.

And NO, a pool cleaner is not expensive to run. Some of the better models cost only 5 cents per hour to operate.

Shocking, checking and adjusting pool chemistry may seem to be a little confusing the first time you do it. But honestly, it’s not very difficult if the read and follow the instructions carefully.

In a world where millions of people do not have access to potable water, a swimming pool is an elusive luxury. Enjoy it responsibly 

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Jeff L. & The Team

Jeff L.

Jeff has been an avid swimmer as long as he can remember, with his first swim lessons in Kindergarten in the 1980s, and became obsessed with pools and swimming shortly thereafter.