How does water hardness effect my hot tub?


Many people are familiar (particularly if you live in the south and east of the UK) with hard water the effects it has on your pipes, appliances, and hot water cylinders. Usually viewed as a problem, hard water can potentially cause expensive damage which is often used to sell a wide range of water softening devices and treatments.

However, contrary to the above, the industry advice is to never use water from a water softener to do a complete fresh fill of your hot tub or swim spa. It is important that the water used to fill your hot tub or swim spa contains a certain level of hardness (or calcium level, to be more accurate) as it is required to make sure that the quality of your hot tub or swim spa water remains at optimum levels. This will also ensure that the swim spa or hot tub's equipment is kept in tip top condition.

High calcium levels (common in water abstracted from ground sources) can lead to scaling and scale deposits forming, as well as cloudy water. Low calcium levels can cause foamy water and corrosion of metal surfaces within your hot tub or swim spa. Calcium levels should be maintained at an ideal level of between 200mg/l – 400mg/l (or ppm – parts per million).

The best time to test your hot tub or swim spa for calcium hardness is immediately after it is filled, whilst the water is still cold. Most treatment products for increasing calcium levels work more efficiently in cool water than they do in hot. We recommend you test the calcium levels every time you freshly fill your hot tub or swim spa.


If you need to increase your calcium levels if you live in a soft water area, our Jacuzzi® Hardness Increaser is the product you need! When balancing the calcium levels, we would suggest waiting two to three days before retesting, as these products can take a while to fully dilute. If you accidentally add too much Hardness Increaser, simply drain 6" to 12" (150mm to 300mm) of water, top back up with fresh water, and retest.


There are no chemical products on the market for reducing calcium levels, however if you live in an area with very hard source water there are a couple of things you can try to reduce the calcium levels in your hot tub or swim spa.  If your house is fitted with a water softener, then try filling the hot tub with regular tap water up to 6" to 12" (150mm to 300mm) below the fill level, then fill the final 6" to 12" using water which has passed through the water softener. Important note: this is the only circumstance we recommend you can use softened water in your hot tub. If you are unable to reduce high hardness levels, don't worry. Just make sure your pH and alkalinity levels are kept in balance. You can also use a hot tub scale inhibitor, such as the Jacuzzi® No Scale, to lower the chance of scale precipitating out.

As always, if you have any questions or queries about swim spa or hot tub chemicals feel free to get in touch with our team on 01276 477461 or !