How to shock a hot tub or spa: what you need to know

Want to know how to shock a hot tub as part of your spa maintenance regime? Here’s what to do

how to shock a hot tub by pouring in chemicals
(Image credit: ClearWater)

It’s vital to know how to shock a hot tub because it’s part of the sanitization routine you should follow. Shocking the tub means adding the chemicals that keep the water clean, and bacteria and contaminants at bay.

Once you’ve finalised the design of your hot tub ideas and chosen the right model to suit your needs, adopting the right cleaning and maintenance regime for your spa is a must so it’s always a pleasure to use. Skip the task and the water can start to look nasty and is even potentially harmful to bathers.

The good news is that shocking a hot tub is an easy process, and we’ve got the lowdown for you along with advice from the experts so you can keep the water sparkling clean.

How to shock a hot tub

Once you've invested in one of the best hot tubs, the issue of how to shock a hot tub or spa comes up for important reasons. ‘Shocking your hot tub could mean the difference between a pleasant bathing experience or the start of bacteria,’ says Tim Snelling from Hot Tub Hub

It’s a straightforward task, however, that involves adding chemicals to the water. ‘The sanitizer added to the water is put there to kill bacteria and viruses that could be potentially harmful to bathers if left to multiply unchecked in warm water,’ explains Sallie Leslie-Golding from BISHTA (The British and Irish Spa and Hot Tub Association). 

‘Other organic contaminants can find their way into hot tubs, such as cosmetics, deodorants, detergents, etc. This can make the water look cloudy, murky, uninviting, and can sometimes lead to foaming. These contaminants are dealt with by a process called “shock dosing” or “oxidizing” to give it its correct terminology.’

Just as with how to clean a hot tub, there are some simple steps to follow if you need to know how to shock a hot tub.

1. Add the shock treatment

A shock treatment needs to be added to the filled hot tub. ‘There is a wide range of shock treatment products available on the market, some of which are chlorine-based and some of which are non-chlorine treatments,’ says Sallie Leslie-Golding.

‘They are simply measured out and added to the water, following the instructions on the manufacturer’s packaging. Some shock dosing treatments are produced in sachet form containing pre-measured one-shot doses to make the process even more easy and convenient.’

woman pouring chlorine into a hot tub

(Image credit: ClearWater)

2. Test the water

The process of how to shock a hot tub is easy, but it is vital to test the chlorine or bromine levels in the water before you use the spa again. You may need to add chemicals to restore the correct levels. 

testing the chemical levels in a hot tub before use

(Image credit: ClearWater)

How often to shock a hot tub

Shocking a hot tub is a process you need to carry out regularly. ‘A shock treatment should be carried out routinely once a week,’ says Sallie Leslie-Golding. 

But be aware that you may need to do it on other occasions as part of your hot tub maintenance. ‘Additional shock dosing should be done after periods of heavy use, after a loss of water quality or at the first signs of algae or slime,’ says Tom Drakett-Cain, brand marketing manager at Lay-Z-Spa.

Followed the steps in the guide on how to drain a hot tub, cleaned and refilled the spa? ‘Shock dosing a hot tub’s water should always be done when filled with fresh water,’ says Tom.

Hot tub shocking mistakes and how to avoid them

We asked the experts which mistakes they see when owners are discovering how to shock a hot tub. These are the pitfalls, so you can swerve them.

  • Miscalculating the dose
    ‘Mistakes can be made by not shock dosing with the correct amount of chlorine in relation to the volume of water,’ says Tom Drakett-Cain. ‘Too little means it won’t be effective enough and too much means the chlorine levels will remain too high to use the hot tub for quite a while. We always recommend following the instruction provided with ClearWater chemicals.’
  • Getting back in the water too soon
    ‘It is important to ensure you leave the shock enough time before reusing your hot tub,’ says Tim Snelling of Hot Tub Hub. ‘This time depends on the sanitizer that you use to shock, so it is essential that you test the water to ensure the levels are safe to enjoy using your hot tub again.’

If you're using your outdoor spa in winter, don't forget that you'll also need to consider hot tub winter care to ensure your spa is fit for use all year long. 

Sarah is a freelance journalist and editor writing for websites, national newspapers, and magazines. She’s spent most of her journalistic career specialising in homes – long enough to see fridges become smart, decorating fashions embrace both minimalism and maximalism, and interiors that blur the indoor/outdoor link become a must-have. She loves testing the latest home appliances, revealing the trends in furnishings and fittings for every room, and investigating the benefits, costs and practicalities of home improvement. It's no big surprise that she likes to put what she writes about into practice, and is a serial house revamper.