Pool Spa Life
Pool Spa Life

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Autumn's cooler days and longer nights are perfect for lazing in the spa. Just as swimming pools need maintenance and upkeep, a little attention will keep your spa in tip-top condition and see you through the chillier months.

Owning a spa pool or hot tub requires a little regular maintenance to ensure effective operation and to provide clean and healthy water.

Recommended water treatment for spas differs from swimming pools as hot water provides a breeding ground for viruses, bacteria and algae if left unchecked. You’ll need to utilise chemicals in order to maintain appropriate levels, regularly checking the total alkalinity, pH and sanitiser (either chlorine or bromine) levels.

Changing the water

For spas, depending on your usage, you may need to replenish the water 3-4 times per year. Alternatively, you can implement a system of remove and replace, draining and refilling about one third of the volume every three to four weeks.

Total alkalinity

Your spa’s total alkalinity level should fall in the range of 90–150 parts per million (ppm). Low alkalinity is a problem because it causes rapid pH fluctuations, which can lead to damaged surfaces and corrosion. It also makes it difficult to balance phosphates, which makes it easy for algae to survive and turn the water green. High alkalinity can also lead to green water as chlorine effectiveness is compromised, allowing algae to thrive.

Adding sodium bicarbonate in small quantities will raise total alkalinity and adding small quantities of hydrochloric acid will lower levels. In both cases, wait one hour and retest the water.

pH level

pH is the scale used to measure acidity or alkalinity in your spa water. It’s important to maintain the optimum pH level, as deviations affect the performance of other chemicals. pH is measured on a scale of 0 to 14, where 7.0 is neutral, less than 7.0 is acidic and greater than 7.0 is alkaline.

Variations in pH lessen the efficacy of sanitisers (chlorine or bro-mine) and can cause eye and skin irritation, cloudy water, corrosion of spa fittings and formation of scale on interior surfaces and fittings. When measured at room temperature — not hot — spa water should always be above 7.0 to avoid corrosion. It should not, however, be higher than 7.8, above which sanitisers are compromised.

To increase pH levels, add small amounts of soda ash; to de-crease, add small amounts of hydrochloric acid. In both cases, wait one hour and retest the water.


Sanitising is an essential practice to ensure safe, healthy water that is free of harmful microorganisms. The most common forms of sanitiser are chlorine and bromine, with some spas also utilising ozone in conjunction with one of the two main types.

The amount of disinfectant required depends on a number of factors including water temperature, frequency of use and the number of spa users. Sanitiser levels should always be at 2 to 3 ppm. Sanitiser is consumed very quickly in high water temperatures, so levels should be checked regularly while the spa is being used.

Your spa water should be shocked-dosed with sanitiser on a weekly basis, or after heavy use. Check the label of your sanitising product or consult your spa or pool shop professional for further information on shock dosing. Be sure to re-check levels before using the spa.

if your spa or hot tub is not being used, add sanitiser every day to prevent contamination.

Recommended levels

Ensuring that optimum pH and sanitiser levels are maintained will keep your spa free of viruses and bacteria:

  • total alkalinity: 90–110 ppm

  • pH: 7.4–7.6• Chlorine: 2–3 ppm

  • bromine: 3–4 ppm

General considerations and Safety

To maintain hygiene standards, it’s important to keep the filter and pump clean. Check and clean the filter regularly and empty hair and lint from the pump as required.

Naturally, children must be supervised at all times when in or near spas and hot tubs. In general, water and alcohol are not a great mix, so factor that in when planning a warming soak this autumn.

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