Pool Chlorine Vs Shock: What's the Difference?

Pool Chlorine Vs Shock: What's the Difference?

Pool Chlorine Vs Shock: What's the Difference?

Regular doses of chlorine and pool shock treatments are key players in the sanitisation of your swimming pool. Any diligent pool owner will know that without treating your water with chlorine and shock, you end up with improperly balanced, unclean water. 

But as both do similar things, you’d be forgiven for not knowing exactly how they differ and when you may need to use one over the other. Here, we untangle the two and provide some insight into the differences and similarities between traditional chlorine and shock. 

What is Chlorine? 

Chlorine is one of the most commonly-used swimming pool chemicals. It is used to sanitise, oxidise and disinfect pool water, helping remove bacteria, dirt and debris and prevent algae growth. 

Pool chlorine comes in various forms, including non-stabilised and stabilised chlorine granules, tablets and liquids. On a basic level, when your chosen method is applied to the water, chlorine releases hypochlorous acid and hypochlorite ion. These chemicals break down the cellular structures of contaminants and destroy them, leaving your water clean. 

The sun is an enemy to unstabilised chlorine as UV rays can destroy it and prevent it from keeping your pool clean. Stabilised chlorine has cyanuric acid added to it to protect it from the sun and ensure it doesn’t get burnt off. 

Because of the way chlorine behaviours in water, there are several different types of chlorine we talk about: 

  • Free chlorine: the amount of chlorine that is available to sanitise your pool water. This is the level you’ll usually test for, and you should aim for between 1-3 ppm.
  • Combined chlorine: the chlorine that has been used up to clean your water, which is no longer actively sanitising but is still present in the water as chloramine.
  • Total chlorine: the sum of free and combined chlorine. 

What is Pool Shock? 

While pool shock also works to sanitise your water, it is slightly different from using chlorine as part of a regular maintenance schedule. Shock dosing refers to adding a high concentration of chemical sanitiser in one dose to immediately increase the level of your sanitising chemicals and get your pool clean. 

Pool shock does not necessarily always use chlorine as its sanitising chemical (although chlorine shock is commonly used); there are various popular non-chlorine pool shocks too. 

The stronger concentration of pool shock also helps destroy chloramines, which are the waste products created when your regular chlorine does its job of breaking down contaminants. Breakpoint chlorination refers to when there is enough free chlorine in the water to break down chloramine. 

What is the Difference Between Chlorine & Shock? 

The key differences between using chlorine and shock are the concentration of the active sanitising chemicals and the way you actually use the products. It’s unlikely you’d want to use your regular chlorine tablets as a shock as they won’t be able to raise the chlorine levels high enough. 

Using Chlorine

Pool chlorine is good for maintaining a proper chemical balance and generally preventing the water from getting dirty. 

In periods of regular use, you should check your chlorine levels around 2-3 times a week to ensure they are in the proper range, topping it up when necessary. Depending on your pool habits and the type of chlorine you use, you’ll likely have to add new chlorine to your pool around once a week to maintain the proper levels. 

Using Shock 

Pool shock is intended to be used slightly differently, providing more of a ‘deep clean’. Adding shock to reach breakpoint chlorination effectively gets rid of everything unwanted in your pool, resetting the water before the chloramines build up again. 

During the swimming season, you should aim to shock your pool once a week or at least once every two weeks. Shocking your pool can also be particularly useful after pool parties or when you notice signs of algae, as it’ll do a quick job of eradicating lingering contaminants. 

Do You Need Chlorine If You Use Shock? 

Yes, as explained, they perform different functions, so you’ll need both. Chlorine (or a chlorine alternative like bromine) is slow-releasing, providing round-the-clock sanitisation. Shock is quick-releasing, instantly raising chlorine levels but also dissipating more quickly. 

Without the use of everyday chlorine, the chlorine levels introduced by the shock would soon fall, whereas, without the use of shock, the chlorine levels wouldn’t become high enough to eradicate all the contaminants or reach breakpoint chlorination. 

Do You Add Chlorine & Shock at The Same Time? 

You should not add chlorine and shock at the same time, as it’s largely redundant to do so. 

Ideally, you should shock your pool at night, so the sun cannot interfere and destroy the active chemicals before they can do their job. Then, you can add your chlorine post-shock after the chlorine levels have fallen below 5 ppm. 

Hopefully, this sheds some light on which sanitising products you need and why! At 3chlorine Pools, we stock a great range of swimming pool chemicals, including chlorine, shock treatments and non-chlorine alternatives to ensure you can maintain a happy and healthy pool. 

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