man smelling foul water from untreated hot tub

Can You Use a Hot Tub Without Chemicals?


Many new hot tub or swim spa owners are hesitant at the thought of adding chemicals to their water, so we’re going to look closely at what water treatment is, why it’s important and to answer to the burning question:

Do you really need to use chemicals in a hot tub? And if so, why?

The term ‘chemicals’ has inexplicably had a bad rap in recent times, particularly Chlorine, but the fact remains that globally it is still the most commonly-used sanitiser due to its unrivalled efficacy.

Using chemicals in hot tub and swim spa water ensures it is clear and safe for bathers to use. Many types of bacteria thrive in warm water and will rapidly multiply when left untreated, thus rendering a hot tub unsafe to use. The regular use of chemicals prevents such multiplication.

Let’s look more closely at the role of chemicals, together with some frequently-asked questions.

Is your hot tub or swim spa ready to use?

Hot tub and swim spa water should be tested daily to ensure the water is safe to bathe in.

The primary daily tests are:

  • Sanitiser levels – for Chlorine 2 – 3 parts per million (ppm), and Bromine should be 3 – 4ppm
  • pH should ideally be between 7.0 and 7.5

Prolonged exposure to low / no sanitiser readings will significantly raise the potential of harmful water conditions. The water will become cloudy and smell foul, bacteria will start to form and multiply, making the water unappealing and a real risk to bathers.

The water should be tested weekly for Chlorine stabiliser (if using Chlorine), ideally the stabiliser reading (Cyanuric Acid) should be no higher than 50ppm.

Test the Total Alkalinity (TA) weekly, you should aim for an ideal reading between 80 – 150 ppm.

Read our article here for more information on testing your tub and spa water.

Can you use so-called natural products instead?

Claims have been made that chemicals can be replaced with more ‘natural’ or ‘organic’ options.

Some products available may appear to enhance your water, making it feel ‘softer’ or ‘silkier’, but the fact still remains that only chemicals, such as those we discuss in this article, can keep your hot tub or swim spa water free from harmful bacteria and safe for your bathers.

The role of a primary sanitiser: Chlorine or Bromine

A primary sanitiser in hot tubs and swim spas eradicates bacteria and other harmful organisms so that bathing can take place in a safe environment.

To assist the role of the primary sanitiser (Chlorine or Bromine), UV and/or Ozone systems can also help ride the water of more stubborn types of bacteria.

Non Chlorine Oxy Shock should be used for the weekly shock dose process however this shouldn’t be considered a standalone primary sanitiser.

Chlorine Dioxide is being used very successfully and more frequently, and whilst this shouldn’t be used or considered as a primary sanitiser, periodic usage (fortnightly or monthly) is beneficial. It will remove molds and slimes within the hot tub pipework which in turn ensures the primary sanitiser can focus on its main function of killing bacteria.

What happens if you do not put chemicals in a hot tub?

If the key chemicals are not added on a regular basis and water is generally neglected, the clarity will disappear and unwanted visitors, such as bacteria, will start to multiply making the water unsafe for bathing.

The key chemicals added to hot tub water are the sanitiser (chlorine or bromine) and pH balancers (pH Plus or Minus); weekly shock dosing is also vital.

What happens if you use an untreated hot tub?

There are very unpleasant and dangerous bacteria that thrive in untreated hot tub water, these pose a real threat to health and the safety of the bathers.

We would recommend that a hot tub is never used unless its water has been tested and appropriate chemicals added.

How long can untreated water sit in a hot tub?

Untreated hot tub water could potentially start to harbour and multiply bacteria immediately after being added to the tank. For this reason alone it is imperative to test it and add appropriate chemicals before it is used by bathers.

Is Bromine the same as Chlorine?

Bromine and Chlorine are different.

Both have their own chemical symbol in the periodic table, Chlorine being Cl and Bromine is Br.

Chlorine creates Hypochlorous Acid in water, whereas Bromine creates Bromochlorous Acid in water.

Can I mix Chlorine and Bromine?

Do not mix chemicals, such as Bromine with Chlorine, as this can lead to a chemical reaction that liberates toxic gases.

It is essential that either Chlorine or Bromine is used as the primary sanitiser and that the two chemistries are never mixed.

Which is better for the hot tub, Chlorine or Bromine?

This tends to be down to personal choice but let’s look at a more detail on both sanitisers.

Bromine works well in warm water, therefore it is ideal for hot tubs. It is much less impacted by pH to work efficiently at killing pollutants (bacteria, etc). However, a negative aspect for bromine is that it tends to be expensive to buy.

Chlorine is probably the most common sanitiser used for hot tubs, it is readily available as fast dissolve granules (the most popular) and also as slow-dissolve tablets. Chlorine is more impacted by the pH balance of the water; high pH readings will reduce the efficiency of the Chlorine.

Can I switch from Chlorine to Bromine in my hot tub?


If you’re wanting to change or switch your primary sanitiser you should completely drain the hot tub or swim spa water, refill it, and then add your new chosen new sanitiser, either Chlorine or Bromine.

Are Bromine tablets or granules better?

Bromine tablets dissolve slowly and will need to placed in a dispenser / erosion feeder; the water flowing over the tablets in the erosion feeder will release the Bromine.

Bromine granules are a different chemistry to tablets and tend to be called Brominating Concentrate or Bromine Infused Granules. They dissolve quickly and are either used to shock dose the water or are a quick method to raise bromine levels, assisting the bromine tablets.

One last IMPORTANT word

Please be assured that we don’t say any of this lightly.

Our 35 years of experience working with swimming pools, hot tubs and swim spas has taught us is that there is no viable alternative to using water treatment chemicals in order to keep water safe for bathers.

Happy, safe bathing!

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