How to Balance Hot Tub Water

What is Water Balancing?

Water balancing is the process of maintaining the correct chemical composition of your spa water. Maintaining correct water balance ensures that your chosen sanitiser works to maximum effect.

Correctly balanced water also feels and looks good and protects your hot tub shell and equipment.

Some sanitising products, notably ecoOne and eco3spa, reduce the need to constantly monitor the balance of your water and so make life a lot easier. Never-the-less you should still test your water occassionally to make sure that it isn't too acidic, which would cause damage to your hot tub.

Click here to find out more about the symptoms of unbalanced hot tub water...

Three Steps to Success

There are three simple steps to water balancing. Depending on the composition of your tap water and the sanitiser that you are using all three steps are not always required.

  • Step 1 - Adjust the Total Alkalinity (TA)
  • Step 2 - Adjust the pH
  • Step 3 - Adjust the Total Hardness

Step 1 - Total Alkalinity (TA)

Total Alkalinity a measure of the buffering capacity of the water, that is how well the water can resist changes in pH. It is a function of the alkaline minerals (carbonates, bicarbonates and hydroxides) in your water.

Total Alkalinity is the key to water balancing!

It is pointless worrying about your pH or Total Harness level until you have got the Total Alkalinity to within the correct range, so always start here and try to maintain Total Alkalinity levels within the ranges shown in the table.

Total Alkalinity stabilises the pH and prevents pH bounce. This is important because it minimises the risk of corrosion, scale and bather discomfort caused by incorrect pH. If the Total Alkalinity of your hot tub water is too high you will find it impossible to adjust the pH, if it is too low the pH will fluctuate widely and you may experience water discolouration.

Sanitiser Recommended TA range


80 - 160 ppm (mg/litre)

ecoONE with Chlorine or Bromine

80 - 120 ppm (mg/litre)

Chlorine / Bromine / Spa Frog

80 - 120 ppm (mg/litre)

Step 2 - pH

pH is a measure of the acidity or alkalinity of your water. The pH scale has a range of 0 - 14, with 7.0 being neutral. Water with a pH below 7.0 is acidic and above 7.0 is alkaline. Many factors affect the pH level of hot tub water, including the amount and type of of sanitiser present, the introduction of air, some spa fragrance products and sunlight.

At pH 6.5 the water would be acidic enough to corrode the metal of the spa equipment and would be uncomfortable for bathers. At pH 8.0 calcium in the water forms limescale which can be in the form of tiny particles which gather on surfaces or float in the water and give it a cloudy or turbid appearance.

You should aim to maintain pH levels within the ranges shown in the table.

[NB. You must ensure that your TA is within the recommended range for your chosen sanitiser before you adjust the pH.]

Sanitiser Recommended pH range


7.0 - 7.4

ecoONE with Chlorine or Bromine

7.2 - 8.0

Chlorine / Bromine / Spa Frog

7.2 - 7.8

Step 3 - Total Hardness

Water hardness is the concentration of calcium, magnesium, carbonates and other mineral salts in the water. This is the hardness measurement shown on most test strips.

The hardness of your spa water will be overwhelmingly influenced by the hardness of the mains water supply to your home and that is dependant on where you live and the source (river or ground water) of your supply.

The Total Hardness should ideally be tested on first filling your spa and thereafter at monthly intervals. As water evaporates from the spa the minerals get left behind and become more and more concentrated, consequently the hardness of the water in the tub will increase over time. The recommended Total Hardness range for all sanitisers, other than those based on copper, is 250 - 500 ppm (mg/litre). It is very unlikely that your water will rise above that range, but if it does topping up the spa with tap water at a lower hardness will reduce the level.

If the Total Hardness in the tub is too low (very soft water), etching can begin to occur on the tub surfaces which, over time, will become abrasive and uncomfortable for bathers. Apart from the discomfort, rough surfaces are not good because they also increase the likelihood of problems with biofilm growth and make cleaning more difficult.

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