Learn more about recreational water illnesses (RWIs) and how to protect yourself and your family when swimming. Protecting swimmers and their families from RWIs is the reason that water quality standards such as chlorine and pH levels should be regularly checked.

The tables below show the chemical standards for chlorine and bromine-based disinfectants. All licensed pools must meet the standard.

All measurements must be made using a calibrated photometer. Domestic pool water testing kits are not suitable in commercial settings.  

Chlorine

Bromine

What does chlorine do?

Chlorine kills germs in pools—but it takes time to work. Therefore, you must make sure chlorine is always at the right levels. Learning how to test your pool water allows you to know if chlorine levels are too high or too low. If there are a lot of bathers, testing is needed more often. Listed below is some helpful information that will assist you to understand how to use chlorine-based sanitisers.

• Free available chlorine (FAC). The chlorine in chlorinated water that has not yet reacted with anything and is still available for disinfecting. Make sure your test kit can measure FAC.
• Combined available chlorine (CAC) or chloramines. The chlorine in the water that has reacted and combined with contaminants in the water. Chloramines can cause eye irritation and chlorine odours.
• Total chlorine. The sum of both the free available and combined chlorines.
• Forms of chlorine used in pools. Sodium hypochlorite (liquid bleach), calcium hypochlorite (granular or tablet), chlorine gas, chlorinated isocyanurates.
• Milligrams per litre (mg/L) Measurement that is used to measure chemicals in a pool.
• Shock treatment. Adding a large amount of an oxidising chemical to water to destroy ammonia, nitrogen-containing and organic contaminants. Adding chlorine as a shock treatment can also control algae and bacteria but read the label to make sure that your product can do this.

Carefully read and follow the instructions printed on the chlorine treatment package.

Why does chlorine need to be tested regularly?

All sorts of things can reduce chlorine levels in pool water. Some examples are sunlight, air, debris and material from swimmer’s bodies. That’s why the levels must be regularly checked. However, the time it takes for chlorine to work is also affected by the other part of the disinfection team, namely pH.

Why is pH important?

Two reasons, first, the germ-killing power of chlorine varies with pH level. As pH goes up, the ability of chlorine to kill germs goes down. Also, a swimmer’s body has a pH between 7.2 and 7.8, so if the pool water isn’t kept in this range, then swimmers will feel eye and skin irritation. Keeping the pH in this range will balance chlorine’s germ-killing power while minimising skin and eye irritation.

Shock Treatment

A strong chlorine smell does not mean there is too much chlorine in the pool but actually means that a super dose of chlorine (shock treatment) may be needed to correct the problem.

Shock treatment adds a large amount of oxidising chemicals to pool water. This bigger dose destroys organic contaminants and oxidises ammonia and nitrogen compounds which removes the irritating chloramine odour and if chlorine is used, , to sanitise the water as well. Many chlorine shock products also have instructions for destroying algae and bacteria, which can be an added benefit. Shocking should be done with the pump and filter operating, but after sundown to avoid the loss of chlorine to the sun’s ultraviolet rays.

Super chlorination is another term that is sometimes used for shock treatment with chlorine products when 5 or more mg/l of FAC is added. This mode of shock treatment – in addition to oxidising undesired waste – is used to rid the pool of algae and bacteria that might grow in filters and hard-to-sanitise areas. Super chlorination also stops chloramine odour. Super chlorination should reach breakpoint chlorination - when there is enough extra chlorine to consume the irritating chloramines and the test for free available chlorine and total chlorine will give the same value.