How to Balance Spa 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 sanitizer works to maximum effect.

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

Some sanitising products, notably ecoOne and AquaGarde, reduce the need to constantly monitor the balance of your water because, to a cetain extent, they self-regulate the water. Never-the-less you should still test your water at regular intervals. Then, if something does go wrong you'll be able to correct it quickly before it becomes a problem.

Three Steps to Success

There are three simple steps to water balancing, which are described below. In fact, all three steps are not always required since the requirement for water balancing very much depends on the composition of your tap water, the sanitiser that you are using and the contaminants that you unwittingly introduce onto the water:

SanitiserRecommended TA range

Active Oxygen

80 - 160 ppm (mg/litre)

AquaGarde

80 - 160 ppm (mg/litre)

BaquaSpa

80 - 120 ppm (mg/litre)

ecoONE

80 - 120 ppm (mg/litre)

Chlorine / Bromine

80 - 120 ppm (mg/litre)

PristineBlue

30 - 90 ppm (mg/litre)

  • 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.

SanitiserRecommended pH range

Active Oxygen

7.0 - 7.4

AquaGarde

7.2 - 7.6

BaquaSpa

7.2 - 7.8

ecoONE

7.2 - 8.0

Chlorine / Bromine

7.2 - 7.8

PristineBlue

7.0 - 7.4

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 sanitizer present, the introduction of air, some spa fragrance products and algae.

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.]

SanitiserTotal Hardness range

Active Oxygen

250 - 500 ppm (mg/litre)

AquaGarde

250 - 500 ppm (mg/litre)

BaquaSpa

200 - 400 ppm (mg/litre)
(measured as Calcium Hardness)

ecoONE

250 - 500 ppm (mg/litre)

Chlorine / Bromine

250 - 500 ppm (mg/litre)

PristineBlue

less than 250 ppm (mg/litre)
(measured as Calcium Hardness)

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.

[NB If you are using a copper-based sanitizer such as PristineBlue or a biguanide based sanitizer such as BaquaSpa it is the Calcium Hardness, not the Total Hardness, that you must measure. The Calcium Hardness is the element of the Total Hardness attributable directly to Calcium Carbonate and it is specifically the calcium ions that bind to copper ions to reduce the capability of the PristineBlue to work effectively.]

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 algae growth and make cleaning more difficult.