What exactly are the chemicals you need to use to keep the water in your spa or hot tub clean, clear and bright.

Spa chemistry and sanitization.

The relative warmth of the water in a spa added to the fact that it is quite a small volume of water compared to a swimming pool means that maintaining the water’s chemical balance and sanitisation is important.

The filter will do a certain amount of the work towards clarity but in order to keep the water healthy and pleasant for the bathers and avoid corrosion and damage to the spa itself means looking after the water balance with chemicals.

You might not have enjoyed chemistry at school; you might not have understood it. That doesn’t mean that you can’t look after your spa.

There is an entire industry dedicated to making it easy for you to enjoy relaxing in your spa and they make a very good job of it. What is off putting is that they have to use words like; sanitise, spa shock, pH and total alkalinity.

Words that don’t sound ‘easy’ at all… but they are.


The warmth of the spa water combined with perspiration and body oils from the bathers make the water in your hot tub a potentially ideal environment for bacteria to grow in.

Sanitisers are used to disinfect the water and keep it looking and smelling fresh. The two most commonly used are chlorine or bromine.

Your Sundance dealer can provide test strips for either of these two spa chemicals.

If you use chlorine as a sanitising agent then the ideal level is between 1.5 – 3.0 Parts per Million (PPM).

If you use bromine then the correct dosage is between 3.0 – 5.0 PPM.

There are advantages and disadvantages to both chemicals although they do the same job. Bromine is a little more expensive but you will tend to use less of it.

Spa shock.

When people talk about ‘shocking’ their spa or hot tub they are talking about adding a larger than usual dose of chlorine or non-chlorine compounds that will burn off the dead bacteria that have been killed by the sanitisers.

The dead bacteria can make the water look cloudy and shocking your spa will get the water back to its clear state very quickly.

The process is called oxidation.

PH balance.

Getting the pH levels right is one of the most important jobs that pool chemicals have to achieve.

If the pH levels get too high then the sanitisers won’t work effectively and the water will become cloudy. High pH will mean that lime scale can form, just like it does in a kettle in hard water areas, and that can damage your pump, your heater element or block your filter. High pH will even cause skin irritation in some cases.

If the pH levels get too low then that also stops the sanitisers working efficiently and some metal parts of your spa – such as the heater element – may be subjected to corrosion.

Ideally the water in your spa should have a pH balance somewhere between 7.2 – 7.8.

Your spa supplier will be able to provide test strips which make pH a very simple thing to check and chemicals to raise or lower the pH level.

Total alkalinity.

The total alkalinity is the buffer of pH, if it is not balanced correctly, the pH test will not give you a correct reading. Total alkalinity is the ability to control pH.

If the total alkalinity is too high then it becomes hard to change the pH levels in your spa, scale starts to form again, the water gets cloudy and sanitisers don’t work as well as they should.

If the total alkalinity is too low then it’s hard to get the pH level to remain where you need it to be and corrosion can start to occur on metal parts of the spa.

Total alkalinity is measure in Parts per Million and you want to see a reading of 80 – 120 PPM when you test the water.

The levels of total alkalinity can be adjusted with the same chemicals you used to address the pH levels.

Calcium hardness.

Calcium hardness is a measure of the amount of minerals in your water including calcium and magnesium.

The water in your spa needs to have some level of hardness; if the water does not have enough calcium, the water will draw from other minerals, including copper, aluminium and iron and it will get those minerals from the heating elements, pump seals and pipe work in your spa. That will result in equipment corrosion.

If there is too much hardness, you will see scale formation on the spa’s interior and the water will take on a cloudy appearance.

There are test kits and strips for calcium hardness available from your Sundance dealer and if you have a low reading there are calcium booster chemicals.

The level you are aiming to get would be between 100 – 250 PPM.

Balancing the water in your spa.

This might all seem very complicated but the basic principles are quite straightforward and once you have a little experience it will become second nature.

Checking the water daily while your spa is in use, shocking it after heavy use or if it’s not been used for a while and having a thorough check every few weeks will keep water qualities listed above within acceptable limits.

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