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NeedtoKnow Guide on the Use of Pool Chemicals

It is essential to add the correct pool chemicals to your swimming pool since they not only sanitise the water by killing nasty micro-organisms which cause disease, they keep the pool water looking attractively clear.

The following guide will explore some key ins and outs of swimming pool chemicals to help you understand how best to go about it.

Common Types of Pool Chemicals and Their Uses

These types of chemicals are popular for treating swimming pool water:

  • Sanitizers – these are disinfectants which destroy harmful bacteria and other contaminants. Chlorine is the most common solution as a sanitizer.
  • Chlorine Stabiliser – prevents unnecessary loss of chlorine.
  • Algaecide – kills and prevents the growth of algae.
  • Soda Ash (sodium carbonate) – also called pH Plus, this is used to increase the pH level of the pool water.
  • Sodium bisulphate – also called pH Minus, this is used to decrease pH levels.
  • Filter Aids / Flocculants / Clarifiers – these remove debris from your pool.

Sanitization Explained

It is vitally important to sanitize (disinfect) your pool to prevent the spreading of infectious disease as well as the growth of bacteria and algae. In a nutshell, this ensures the healthy condition of your pool.

Sanitization methods include filtration to remove pollutants, disinfection to kill infectious micro-organisms and human hygiene to prevent the introduction of pollutants. Regular testing of your pool water and pH levels is also crucial.

Chlorine and Bromide

The most commonly used methods of sanitization are chlorine and bromine. These oxidizers effectively disinfectant pool water by killing related bacteria. They are economical, easy to use and provide a residual level of sanitizer which remains in the water to protect swimmers.

Chlorine releasing compounds are by far the most popular sanitising method for swimming pools, while bromine is becoming more popular in spas and hot tubs. Both are from the halogen family, meaning they have the ability to destroy a wide range of dangerous bacteria and viruses. They are fast acting, have a strong oxidising effect on pollutants, provide a residual for extra safety and are effective algaecides.

Chlorine compounds break down rapidly in sunlight however, so to extend their disinfectant life they can be supplemented by cynuric acid, which is a granular stabilizing agent capable of extending the residual half-life by four to six times.

It’s important when using chlorine however to understand that you need to use the recommended levels, since overly high amounts can lead to side effects such as sore eyes, skin irritations, fading swimming costumes and even green hair.

Alternatives to Chlorine

Two of the most widely used alternatives to chlorine in swimming pools are:

UV Filtration

Ultraviolet light can be used to irradiate the water to kill existing bacteria. However it has no residual properties, meaning it won’t disinfect any new bacteria introduced into the pool.


It is well documented that ozone kills bacteria and is 300 times more effective than chlorine. However ozone also does not have a residual life and the technology is not yet widely sold to the general public.

Bear in mind that both of these alternatives should be used with a low level of chlorine in the water so as to meet safety standards, but nevertheless they are ideal for the prevention of over chlorination and its side effects.

Tips for Maintaining Your Swimming Pool Water

Even when pool water appears crystal clear, this does not mean that it is healthy. Here is some key information on maintaining your pool effectively:


pH is the scale used for measuring your pool’s acid or alkaline levels and is the most important factor in balancing your pool water. It is measured on a scale of 0 (strong acid) to 14 (strong alkaline), while neutral pH is 7.

The ideal level for pools is at the slightly alkaline level of 7.2 to 7.6 , since this provides optimum use of free chlorine while ensuring it is not corrosive or scale forming. If the pH falls below 7 it is too acidic and can cause eye and skin irritations, corrosion and rapid loss of alkalinity. If the pH is too high (above 8), chlorine activity is slowed and becomes inefficient, scale formation and discoloration of pool walls can occur, water becomes cloudy and all this will overwork the pool filter.

Total Alkalinity (TA)

This is the measure of water’s resistance to changes in pH, thus it affects and controls pH. To put it another way, TA is the amount of alkali (not to be confused with alkaline) in the form of bicarbonates, carbonates and hydroxides present in your pool water. The ideal level for TA is between 80 and 140 parts per million (ppm).


To ensure that your pool water is a safe and clean you will need to test the water regularly and if required, adjust the necessary pool chemicals.

There are several types of testers available:

  • Test Strips (Litmus paper) – these are the simplest and quickest means of testing your pool water for chlorine and pH levels.
  • Liquid Reagent – care needs to be taken with this type of test kit to ensure the correct amount of reagent is added.
  • Test Tablets – these kits are probably the best means of testing your pool water; since they offer simple, accurate analysis at an affordable price.

You should check your pool water daily for both sanitizer and pH. Total alkalinity should be tested on a weekly basis, while water hardness should be tested on a monthly basis.


Maintaining your swimming pool may seem daunting in the beginning, however if you break it down to the basics and choose the correct pool chemicals you will be able to enjoy your swimming without too much fuss.

About the Author: Andrew Astonville is an independent advisor on pool chemicals.


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