How to Use Swimming Pool Shock Treatments

Keeping on top of your chemicals is an essential part of good pool maintenance. Along with regular doses of sanitising chemicals and water balancers, you’ll also need to use swimming pool shock treatments to help keep your water clean and crystal clear. 

Here’s everything you need about what pool shock is, why you need it and how to use it in your pool. 

What is Swimming Pool Shock?

Shock dosing your water is when you add a stronger concentrate of swimming pool sanitiser to instantly get those chemical levels up, providing what can be thought of as a ‘deeper clean’ when compared to general maintenance. 

Shock treatments effectively kill algae, bacteria and other harmful pathogens, as well as breaking down the waste products generated by your sanitiser. They are essential chemicals for when you need to deal with green or generally dirty water. 

Pool shock treatments usually use chlorine as the sanitiser, but this is not necessarily always the case, as there are chlorine-free shock alternatives that accomplish the same results. 

A shock dosing chemical, chlorine or otherwise, differs quite significantly from general day-to-day sanitisers. This is important to be aware of, as you will need to ensure that you're purchasing the correct chemical and using it appropriately.

Pool chlorine vs shock: what's the difference

How Does Chlorine Pool Shock Work? 

Using a chlorine shock treatment raises the water’s free chlorine level. Free chlorine refers to the amount of chlorine in your water that is actively sanitising it. Chlorine works by attaching itself to materials such as algae or dirt. This starts the process of creating free chlorine molecules, which can kill off the algae and other contaminants. 

Dosing your pool with shock to increase the free chlorine levels is essential, as it removes the combined chlorine (the chlorine that has been used up by cleaning the water), which builds up over time as the waste product known as chloramine, which no longer actively sanitises your water.  

Ultimately, using pool shock can help get your free and combined chlorine levels back on track, ensuring your regular chlorine doses can do their job effectively. 

Is Shocking a Pool Necessary? 

Yes – you cannot rely on your everyday sanitisers to maintain the correct chemical levels because they aren’t concentrated enough to break down waste products and more problematic instances of algae growth. 

To keep your swimming pool clean and safe to swim in, you will need to maintain a regular chemical routine that incorporates the relatively frequent use of pool shock treatments – particularly during periods of heavy use. 

what chemicals do you need for a swimming pool

When to Shock a Pool

There are many times it may be necessary to shock your pool. It is not only an essential part of good general water maintenance but is also an effective means for tackling various issues, like algae infestations, reopening your pool after a significant closure or cloudy water. 

Signs You Need to Shock Your Pool

Keep an eye out for the following things as they are surefire signs or reasons your pool is in need of a shock treatment: 

  • Green water or other signs of algae growth
  • Murky, cloudy or foamy water
  • Strong chlorine smell (a sign of increased combined chlorine)
  • When opening your pool
  • After heavy rainfall or exposure to other environmental contaminants
  • After particularly heavy use, like a pool party

Any time you think your pool is a little dirtier than it should be, it’s probably worth testing your water and adding shock if the levels aren’t quite right. 

How Often Should I Shock My Pool

This will depend on the above factors too, but when incorporating shock into your pool maintenance routine, a good rule of thumb is to use it around once a week. 

Shock dosage advice for swimming pool owners

What is the Best Way to Shock a Pool? 

Pool shock comes in several forms, and there are many brands to choose from. Which one you should choose will often depend on your circumstance, but they all fulfil a similar purpose.

Granules Vs Liquid Shock

Liquid shock, or sodium hypochlorite, is fast-acting and does not need to be pre-dissolved like some granular products. It is more commonly used for commercial pools, so it might not be the right choice for domestic pool owners. The shelf life of liquid shock can also be shorter than other options. 

Granular shock tends to be the most popular shock option. While some may need to be dissolved in water, applying these granules is generally very easy and getting the dosage right is quite straightforward. Chlorine granules are also easier to store and have a longer shelf life. 


Chlorine Vs Non-Chlorine Alternatives 

Again, the difference here is based on preference rather than their effectiveness. As with everyday swimming pool chemicals, you may choose to avoid using chlorine as it can cause discomfort for certain bathers with sensitive skin, opting instead for non-chlorine pool shock granules

However, if you already use chlorine in your pool, a chlorine-based shock treatment is more often than not a slightly cheaper option.

How to Shock a Pool 

Shocking your pool is a relatively easy process, especially if you’re already somewhat familiar with using swimming pool chemicals. 

A water droplet in a pool

Test Your Water

Before adding anything, you’ll need an accurate reading of the current chemical levels – the free chlorine level should be lower than the total chlorine level pre-shock. You will also need to review the pH and calcium hardness before adding new chemicals. Check out our guide on how to balance your pool water for more insight into these levels. 

Prepare Your Shock

Carefully read the instructions that come with your shock. This will help you determine how much you need to add and whether it needs to be dissolved in a bucket of warm water first. 

Add Your Shock to the Pool Water

 Add your shock to your pool as per the manufacturer’s instructions. Do so by slowly walking around the perimeter of the pool while pouring in the shock. 

Your pump should be running to ensure the chemicals are thoroughly distributed throughout the system – keep your pump running for around 8-12 hours after adding the shock dose to ensure even distribution. 

Ideally, you should shock your pool at night as the sunlight won’t have a chance to burn off the chlorine. 

How to Use a Shock Treatment Safely

Given the concentrated nature of shock treatments, special care should be given when using these chemicals.

Handle the Product in a Ventilated Area

Ultimately, chlorine is a harmful gas. Handling it in concentrated quantities will release chlorine into the air, so you must be outdoors or in a ventilated space when using these products.

It’s a good idea to wear protective gear like goggles and gloves to minimise potential harm from handling the chemical. 

Clean the Pool Beforehand

Before administering a shock treatment, any detritus, such as leaves, should be removed as chlorine will focus on eliminating floating debris when present. Try to remove visible dirt with nets and pool vacuums before using shock, so it doesn’t have to work as hard to get your water pristine. 

Never Mix Pool Chemicals 

Don’t mix your pool shock with other chemicals, as this will likely result in unforeseen, dangerous chemical reactions.

Rebalance the Pool Before Swimming

You must not swim in the pool until the shock has been properly distributed in the water, as the chlorine levels can be dangerously high. 

Once the chlorine levels have returned to a safe level, the pool will likely need rebalancing. Some pool shocks can change the calcium or pH levels of your water; this will need to be checked and rebalanced before you go for a swim.

Children jumping into a pool

How Long Should You Wait to Swim After Shocking a Pool? 

After using a heavy granular chlorine shock, your pool will usually require 24-48 hours before the chlorine level has dropped to a safe swimming level. Lithium and non-chlorine shock products usually allow bathers to return to the pool slightly sooner; however, you will need to check the manufacturer's instructions before doing so.

If your free chlorine level is below 5 ppm and your pH level is below 7.6, then you should be safe to re-enter the water – but, again, always double-check the product’s instructions! 

Ultimately, pool shock really is a great weapon in your pool maintenance arsenal, and it’s important you know how to use it properly. Hopefully, we’ve answered all your shocking questions – if you need any sanitising chemicals, we stock plenty of options to get your pool looking its best.