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Salt Chlorinators and Bromine Generators
This factsheet outlines some invaluable information regarding the use of salt
chlorinators and bromine generators in hot tubs and especially in swim spas.
What is the difference between a salt chlorinator and a bromine generator?
Salt chlorinators produce sodium hypochlorite from sodium chloride (salt) while salt bromine generators
produce hypobromous acid from sodium bromide (salt family).
Why use a salt chlorinator (or bromine generator)?
Hypochlorous acid (or hypobromous acid) can be produced in small amounts from a salt chlorinator (or
bromine generator) to act as a sanitiser.
What are the main benefits?
The improved “feel” of the water is often a factor mentioned by clients as to why they like this type of water
treatment equipment.
Active disinfectant is constantly generated when the water is circulating, but only when the systems are
working correctly and filtering. Note, neither system reduces the need for regular water testing and periodic
adding of chlorine or “shocking” (ideally with a quick dissolving calcium hypochlorite).
It uses fewer chemicals.
Any issues to be aware of?
Salts can cause corrosion of some metallic components, especially if it is an “aftermarket fit”. Always check
with your spa supplier/manufacturer if the warranty will be affected. You will still need to check the pH.
If the system is working correctly, it is constantly producing active disinfectant. However, with a salt
chlorinator, it is important that Cyanuric acid (e.g. 40ppm) is added to combat the effects of UV (from sunlight)
on the chlorine (not required for the bromine generator).
This system is unlikely to be a ‘low cost’ solution.
Depending on the bather loads, the salt chlorinator (or bromine generator) will not be quick to produce new
active disinfectant. Some units are fitted with a “Boost” button but traditional hand dosed “super chlorinating” is
usually the easiest way to maintain safe sanitising residual levels. It is important to recheck pH. (The use of
Calcium hypochlorite will raise the pH).
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The production of hypochlorous or hypobromous acid is totally dependent on the circulation (or filtration pump)
running. This might increase the filter cycles time.
The salt generating cell itself can be adversely affected if the water balance is an issue. Hard water, for
instance can “fur” up the cell to stop its proper function. Alkalinity and high phosphates can also cause
problems. These will need to be balanced or removed before using the salt system.
Are swim spas a better environment than a hot tub for using a salt chlorinator (or bromine
generator)?
Due to the larger volume of water typically found in a swim spa (compared to a hot tub), the temperature and
the reduced bather load per volume of water, swim spas are likely to be more suitable for salt-based systems.
However the comments detailed above will still apply.
Further information
Swim spas using salt chlorinators will require the Free chlorine to be maintained as a residual at 2 – 3 ppm
and the pH within the range 7.0 to 7.6. The salt generators are not usually automatic in the sense that it will
not measure the water and increases hypochlorite production. So, regular monitoring of Free Chlorine and pH
is important and manual addition of chlorine will still be required. Remember that the system will quickly over
dose if too much chlorine is added manually. The correct control of pH is very important to ensure the chlorine
is effective. Three times as much Free Chlorine is needed at a pH of 8 compared with a pH of 7, to give the
same “killing power”.
Spa and swim spas using sodium bromide salt have the same features and operating criteria as the salt
chlorinator, but by producing bromine, the water does not need Cyanuric acid stabiliser. The bromine reading
should be maintained between 2 – 4 ppm; the pH between 7.0 – 7.6. Bromine is not so pH dependent. The
water will need regular ‘shocking’ with a non chlorine shock, typically monopotassium persulfate. The use of
sodium bromide in its own right helps the buildup of hypobromous acid, the effective disinfectant.
Superchlorination with quick dissolving calcium hypochlorite can be used to raise disinfection residual quickly
and also to regenerate spent bromide, but this will raise the pH.
BISHTA reminds its members that no responsibility can be taken by BISHTA, its employees or agents in
respect of any errors or omissions from this factsheet.
This version of M013 dated 14 January 2016