How to shock a pool – 5 steps to safe, algae-free water this summer

Wondering how to shock a pool? Here's how the experts are getting ready for the sunny season ahead

How to shock a pool
(Image credit: Alamy)

The question of how to shock a pool is one that many swimming pool owners may ask themselves at this point in the year. As we sit on the fringe of the hottest months of the year, you may be wondering how to ensure your pool is clean, clear, and safe for bathing – and knowing how to shock a pool is the best way to achieve this. 

This pool idea is one of the most important things you can do to get your garden ready for summer – and with the right advice, the process is refreshingly simple. 

We caught up with the experts who shared the method they are using throughout the summer.  

Why shock a pool?  

pool patio with container citrus tree in garden of paolo moschino and philip Vergeylen

(Image credit: Annaick Guitteny)

While the term 'shocking' may make you think of a dramatic, transformative process, the activity is not as intense as you may expect. 'Shocking' is the process of adding chlorine or non-chlorine pool chemicals into your water – to raise the 'free chlorine' level. This increased level will destroy impurities such as bacteria, algae and chloramines that may make your pool unsafe. 

'Many pool owners shock their pools incorrectly. To kill off stubborn algae, clear cloudy water or open a pool, shocking is usually a multi-day process rather than a one-time event,' says Adrian, an expert from My Perfect Pool. This is the method he uses.

How to shock a pool – 5 steps to success

1. Clean your pool and filter

Adrian suggests beginning by using a pool net to remove debris and brushing the walls with a pool brush. You should then use your best vacuum cleaner to remove any remaining dust or dirt that remains. 

Once you have cleaned the pool, you should move on to the sand and DE filter. The expert says you should backwash them. However, for a cartridge filter, it is best to remove the cartridges and hose them off.

2. Balance the pool chemistry levels

After cleaning your pool, you should balance the pool chemistry levels. 'The ideal pH for swimming is 7.4 to 7.6,' Adrian explains. 'Chlorine will kill off bacteria and algae faster if thepH is around 7.2.' Meanwhile, your stabilizer level should be 30-50 ppm.

You can test these levels with a kit, and you may need an Alkalinity balancer and apH balancer to bring the levels to the appropriate number. 

pergola seating area next to a pool

(Image credit: Future/Mark Bolton)

3. Choose the shock and calculate the dosage

Adrain explains that most products that are marketed as pool shock are made of calcium hypochlorite. 'It's great for most pools,' he says. However, for saltwater pools, the expert recommends liquid chlorine. 

'The dosage of cal-hypois 1to 1.5 lbs per 10,000 gallons of pool water. For liquid chlorine, it's 1gallon per 10,000 gallons of water,' Adrian says. However, the exact dose depends on the product’s strength. 

4. Add the shock at night

Once you know the right dosage, the expert suggests mixing the shock as per the manufacturer’s directions before pouring it around the outside of the pool. 

'It's particularly important to do this at night, so the sun doesn’t burn off the chlorine,' he says. You should then run the pool pump for a few hours (to circulate the shock), then switch it off and leave the pool overnight.

Adrian explains that you may need to repeat this process another 1-3 times, especially if your pool is particularly dirty. 'This is where most pool owners go wrong – they shock only once.

A narrow swimming pool next to sun loungers and a large house

(Image credit: Future PLC)

5. Filter and rebalance the water 

After you finish the shocking process, Adrian recommends running the filter for 24 hours or until the water is clear. You should then retest the water again to check it meets the correct balance.

'When the chlorine level is below 5 ppm, and the pH level is 7.4-7.6, you’re good to swim again,' he says.

Then when your water is safe, you can enjoy experimenting with the perfect pool landscaping ideas for your garden – so you really are garden party-ready.

Megan Slack
Head of Celebrity Style News

Megan is the Head of Celebrity Style News at Homes & Gardens. She first joined Future Plc as a News Writer across their interiors titles, including Livingetc and Real Homes, before becoming H&G's News Editor in April 2022. She now leads the Celebrity/ News team. Before joining Future, Megan worked as a News Explainer at The Telegraph, following her MA in International Journalism at the University of Leeds. During her BA in English Literature and Creative Writing, she gained writing experience in the US while studying in New York. Megan also focused on travel writing during her time living in Paris, where she produced content for a French travel site. She currently lives in London with her antique typewriter and an expansive collection of houseplants.