How To

A guide to using Chlorine in your pool: How It Works & How to Use It

Chlorine is a hugely important ingredient in your pool’s water chemistry — so understanding why you need it, its properties and how to use it effectively is a high priority.

Chlorine, what is it?

Chlorine is a chemical disinfecting agent that comes in either liquid, tablet (solid) or powder form. It is added to pool water for the following reasons.

  • To kill micro-organisms that carry diseases such as E-Coli, Cholera, and dysentery
  • To rid water of bodily fluids, urine, sweat and body oils from people 
  • Eliminate dirt and debris from the wider environment
  • Stop algae growth

Chlorine doesn’t become a disinfectant until added to the pool and reacts with the water, forming ‘hydrochloric acid. this substance combines with the harmful bacteria in the pool to form Combined Chlorine or another name for these is Chloramines.

This chemical reaction works best under the right pH which is why you need to check levels manually or by using an automatic pool controller.

Which is better, liquid, solid or powder?

  • Liquid Chlorine
  • Cheaper
  •  Can be added in large quantities 
  • Ph level of 13, therefore, requires careful balancing of pool water which over time can increase costs
  • Good option for larger volume commercial 
  • Needs to be carefully handled and stored
  • Chlorine Tablets
  • May contain other substances such as algaecide and water clarifier so you will not need to purchase these separately 
  • Better for domestic pool use 
  1. Powdered Chlorine/granules
  • More effort is required as you may need to dissolve before adding to pool water 

The Different Types of Chlorine

Regardless of what form of chlorine you choose, you will need to understand the difference between stabilised and unestablished Chlorine.

  1. Un-stabilised Chlorine 

Chlorine has not been mixed with Cyanuric Acid, a chemical that protects chlorine from the sun’s UV rays. This form of chorine is commonly used in indoor pools. It has a shorter lifespan than stabilised chlorine so can be used in large dosing quantities or to shock your pool in case of an emergency of fast falling levels of chlorine.

To further complicate things, there are 3 different chlorine compounds you can buy that fall into the un-stabilized category:

  1. Sodium Hypochlorite – liquid form and contains around 10-12% available chlorine. It is added to pools through a chemical feeder and is mostly used in large/commercial pools since it can be easily added in large volumes.
  2. Lithium Hypochlorite – Granular form and contains around 35% available chlorine. It has a fast dissolve rate which makes it good for shocking but also prevents a bleaching effect on vinyl and fibreglass pools. It is, however, more expensive.
  3. Calcium Hypochlorite – Granular or tablet form and contains around 60% available chlorine. This is the most popular type.
  4. Stabilized Chlorine

Chlorine that has mixed with cyanuric acid (CYA), protects your chlorine from the sun’s ultraviolet (UV) rays which decreases the overall burn rate of your dosage. Is only relevant to pools exposed to sunlight? You will need to check the levels of CYA over time as the higher these get, the more chemicals you will need to balance out the pool chemicals.

Only 2 different chlorine compounds fall into the stabilized category:

  1. Sodium Dichlor – Granular form and contains around 56-62% available chlorine. Can reduce the pH and total alkalinity of your pool water.
  2. Lithium Trichlor – Powder and sometimes tablet or granular form, and it contains around 90% available chlorine. This is a solid, dry form with the highest chlorine content.

Methods Of Adding Chlorine to Your Pool

Below will cover the 2 methods you can use to add chlorine to your pool, the pros, and cons of each, and which one is recommended.

  1. Manually/ Your Pool’s Skimmer Basket

Adding chlorine to your pool skimmer (preferably tablets) will allow the dissolved chlorine to travel through your filter system and into the pool.

You will need to remove the chlorine from your skimmer when your pump is off, otherwise, you will get a high concentration of chlorinated water which can be corrosive.

  1. An Automatic Pool Controller – Chlorinator

An automatic pool controller – this can communicate with the chemical dosing pump to automatically dose chlorine. Is connected to the filter system and will output as much chlorine as you tell it to via set-point and thresholds on the control panel. This setup will allow you to boost dosage in larger volumes in case of a faecal accident. 

Using an automatic chlorinator is the best method if you can afford the initial investment.

Combined Chlorine

Chlorine reacts with water to form hydrochloric acid but also combines with harmful pathogens in the pool which form combined chlorine also known as Chloramines.

Adding more chlorine to your pool, these chloramines build up which slows down the disinfection rate, causes skin and eye irritation and is responsible for the overpowering smell of chlorine.

The solution is to shock your pool by adding even more chlorine 10 x the chloramine level until the molecules break apart, also known as the oxidation process. This oxidation causes chloramines to gas off and leave the pool.

Using an automatic pool controller will help you reach the right levels of chlorine therefore it is more accurate than manual dosing.

Chlorine Alternatives

Although Chlorine is the cheapest chemical disinfectant on the market and most widely used because if used correctly is completely safe to sanitise your pool. However, it irritates your eyes, dries out your skin, and can create unpleasant ammonia smells. 


It is typically bought in tablet form and functions in much the same way on a molecular level as Chlorine. So equally problematic if not used correctly.

The benefit of using Bromine is that it does not give off a chlorine smell, is better on your skin, and is more effective at sanitizing your pool which means smaller, less frequent top-ups however is slow releasing and more costly.

Because Bromine is un-stabilized It means it may be unsuitable for outdoor pools and has many faster-burning effects of UV than stabilized chlorine. It also works better in higher temperatures which is why it is typically used in hot tubs.

Salt System

Saltwater pools feed salt through a saltwater generator, turning the salt crystals into chlorine. A saltwater pool that uses chlorine as a sanitiser.

The advantage is that you no longer need to buy or handle chlorine chemicals and top them up with salt. The salt system can also communicate alongside an automatic pool controller for auto-dosing. The downside is the upfront costs can be huge.

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