Bromine and Chlorine Sanitisers

Bromine and Chlorine Sanitisers

Chlorine and bromine are two chemicals that are often used to sanitise hot tubs and pools.
But why do we need them in the first place? The answer has to do with bacteria.
Hot tubs provide the ideal conditions for bacteria to grow: a source of food (from the bathers), a warm temperature, and lots of moisture. Without chlorine or bromine, bacteria and pathogens like legionella, pseudomonas aeruginosa, mycobacterium, and cryptosporidium can quickly take over the water. While most of these microbes are harmless, some can cause serious illness. chlorine and bromine help to prevent the growth of these harmful microbes, keeping the hot tub water clean and safe.


Chlorine is the most popular sanitiser on the market. It is an affordable and effective method of sanitising a spa. The ideal chlorine level should be around 3-5mg/l (three to five milligrams per litre).

How does chlorine work?

When chlorine is dissolved, it creates hypochlorous acid. It is this that breaks down the bacteria in the water to create a safe and sanitised environment for bathing. Once the hypochlorous acid has broken the bacteria down, it becomes deactivated. In addition to killing bacteria, hypochlorous acid reacts with sweat, urea, and bather contamination (ammonia).
This is called combined chlorine.

It is the combined chlorine that is responsible for the characteristic chlorine smell of pools and spas, and it is also capable of causing irritation to skin and eyes.

How do we deal with the Combined Chlorine?

UV, ozone, and regular shock dosing are all effective methods for reducing the combined chlorine levels in pool and spa water. UV light breaks down chloramines, while ozone reacts with them to form harmless byproducts. Shock dosing helps to break down combined chlorine, making it more easily removed by filtration. Pre-bathing showers are also helpful, as they remove contaminants from the body before they have a chance to enter the water. For particularly high levels of combined chlorine, a shock dose using an oxidiser can be used to remove it from the water completely. By taking these steps, you can ensure that your pool or spa remains safe and enjoyable for everyone.


bromine is an affordable and effective method of sanitising a spa or hot tub. Many people find that bromine has less odour and is gentler on the skin than chlorine. The ideal bromine level for a domestic setting is 3-5mg/l, while in a business setting it should be around 4-6mg/l. So how does bromine work? When it’s dissolved in spa water, it creates hypobromous acid. This acid breaks down bacteria, creating a safe and sanitised environment for bathing. After breaking down the bacteria, it becomes combined bromine and still retains a small amount of sanitising effectiveness. The by-product is Bromamines, which is not as problematic as Chloromines but regular shocking is still required to tackle it.

Combined Bromine

Unlike chlorine, bromine remains effective even in the presence of organic matter, such as sweat, hair, and lotions. Combined bromine is produced by combining bromide ions with hypobromous acid. When the hypobromous acid reacts with any organic content, it is reduced back to bromide ions. Most of these ions can be reactivated back to hypobromous acid by adding an oxidizer. In order for combined bromine to remain effective, additional bromide salt or ions need to be added periodically to make up for the lost ions. Combined bromine is an effective disinfectant that helps to keep swimming pools and hot tubs clean and safe.

Please note that a bromine sanitised spa cannot be switched over to chlorine easily if there is still bromine in the water. All of the chlorine will be used to convert bromide ions into hypobromous acid. Until the bromide level in the spa falls below 15 parts per million, the spa will be sanitised with bromine, none of it will provide a chlorine residual. Unfortunately, there isn’t a test kit for measuring just bromide ions in the water and so it may take many many weeks for the levels to fall. Draining and refilling the hot tub would probably be the best option here.

Bromine and Chlorine
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Bromine & Chlorine Products
Bromine Chlorine

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Bromine & Chlorine Products

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