We’re back again with another article about keeping your hot tub clean. This time, we’re talking about how to shock a hot tub, as well as why it’s so important to do this. Read on to get all the details.

We’ve written before about dealing with scum, scale and stains, as well as whether you should use chlorine or bromine. Today’s article is about another sanitising task you might not be aware of – shock dosing, or shocking.

Just putting sanitiser into your hot tub isn’t enough to keep the water properly clean. You’ll also need to regularly shock the water in your hot tub by adding special shock formula. Your hot tub manufacturer will provide guidance on how often you should do this, but in general you should do it weekly, or even twice a week if your hot tub or spa gets a lot of use.

What is hot tub shock used for

There are lots of reasons why you should use hot tub shock in your spa. Quite simply, it’s an essential part of keeping the water in your hot tub clean for you and your guests.

Here are some of the key reasons why shocking your hot tub is so vital.

  • It removes contaminants. Purely through normal use of your hot tub, the water will pick up lots of contaminants. From shampoo to deodorant, even dead skin cells and hair – there are a lot of invisible contaminants that can get in the water. Shocking, alongside your regular chemical sanitiser, is a great way to clean these out.
  • Kills bacteria. Along with the organic contaminants that could be left in your hot tub, shocking will also kill off any bacteria that could be growing. Applying hot tub shock just boosts the sanitiser in the water and makes sure your hot tub water is safe.
  • Removes sanitiser by-products. Another key reason to shock your hot tub water is that it removes the by-products that are naturally produced by your sanitiser. Chlorine produces chromamines, and bromine produces bromamines – both are waste products that can be smelly and unpleasant if allowed to build up, so it’s a good idea to get rid of them using a shocking treatment.

Which hot tub shock is best to use?

There are a few different kinds of hot tub and spa shocks that you could use. Always follow your manufacturer instructions here, too, as some brands of hot tubs may recommend certain types of product.

Firstly, one thing to remember is that there are a few options of shock products that are for pools – you definitely shouldn’t use these on your hot tub. You may have heard of “cal hypo”, or calcium hypochlorite, which is a popular pool shock. But, it won’t be very effective at all on water in your hot tub, so ensure you buy a brand of shock that’s specifically formulated to work with the heated water in spas.

In terms of options for your hot tub, there’s two real types of shock that you can use. The first is called dichlor and is extremely common. Dichlor is the active ingredient in lots of brands of hot tub shock, so this will likely be the kind you use in your hot tub. Dichlor will work fine whether you use bromine or chlorine as your hot tub sanitiser.

The other option is non-chlorine shock. This type of shock is generally gentler and less chemical, and it’s not actually a disinfectant, so it won’t kill bacteria by itself. What it does do is remove contaminants by an oxidisation process, and activates free chlorine from your sanitiser – so your sanitiser will work better.

Which type of hot tub shock is best for you will depend on how often you use your hot tub. In general, most manufacturers recommend using a chlorine shock approximately once a week. But, if you don’t use your hot tub very often, you could use a non-chlorine shock weekly and then perhaps a chlorine based on less often.

Finding the perfect regime for your hot tub will take a bit of trial and error, so keep regularly testing your water to measure the sanitiser levels and inspect your hot tub often for signs of any dirt or grime building up. If you do find this, simply shock your hot tub more frequently.

For those with mineral or oxidiser sanitised spas, take care to follow your manufacturer instructions as your shocking regime will be quite different. Or, get in touch with us at BMS spas for specialist advice.

How to shock your hot tub

So, how do you actually go about shocking your hot tub? Here’s our step-by-step guide to the whole process.

Remember that you if your hot tub is outside, you should generally undertake this process in the evening. The sun can cause the shock to burn off too quickly, so you won’t get the full effects.

  1. Remove the hot tub cover. The first step is straightforward – simply remove your hot tub’s cover. Also remove any accessories that may be floating in the water and, obviously, don’t shock your hot tub while people are bathing.
  2. Test the water using your usual method. You should be regularly testing the water in your hot tub, but it’s essential that you do so before and after shocking. Test before you do anything else to make sure that your spa’s pH balance is at the right level, generally between 7.4 and 7.6. If it’s not, the shock won’t work as it should – so adjust it to be sure.
  3. Prepare the hot tub and yourself. Wear appropriate safety gear for handling chemicals like gloves and goggles. Also, turn the jets in your hot tub off – but leave the pump on. The water should be circulating but not too agitated.
  4. Apply the shock treatment. This is as simple as measuring out the right amount of shock (which will vary depending on the amount of water in your hot tub), and then adding it according to the method on the label. Always follow the instructions given carefully.
  5. Now, the easy bit. Just leave the hot tub uncovered for another 20 minutes or so. This will let some of the shock dissipate.
  6. The last step is to test the water before you us your hot tub again. Make sure that the pH has returned to neutral and that the chemical levels have dropped to the normal amount that you target.


Looking for someone to keep your hot tub in tip top condition? Check out BMS Spa’s hot tub maintenance and servicing packages. We’ll take care of all the big jobs – and we can offer you some great advice on how you should be doing the little cleaning jobs, too. Get in touch today.