hot tub chemicals

Ultimate Hot Tub Chemicals Guide 2024

Posted by Alex Clamp in Maintaining a Hot Tub Guides on 16th August 2023

If you own a hot tub (or swim spa) and are looking for a high-quality, straight-to-the-point guide on how to maintain your hot tub’s chemical balances, you’re in the right place!

Keeping hot tubs topped up with chemicals is key in making sure the sanitiser you add works and it stays hygienic, so read on to find out everything you need to know about hot tub chemicals.

Everything You Need to Know About Hot Tub Chemicals

hot tub chemicals

“Hot Tub Chemistry” might sound daunting, but it’s really just a matter of keeping your hot tub topped up with a few different chemicals to keep it clean.

There are three things you’ll be adjusting with those chemicals: Total Alkalinity (TA), pH, and Total Hardness (TH).

Get to grips with these three parts of hot tub chemistry and you will be able to troubleshoot any problems you have with your hot tub’s water, like cloudy or foamy water.

Total Alkalinity

Total Alkalinity (TA) measures the total amount of alkalinity in the spa water.

Alkaline neutralises acid, so your hot tub’s water will irritate your eyes and skin if not regulated properly. Alkalinity levels that are too low can even erode your spa’s components e.g., the pump, due to scale build-up.

Your hot tub, therefore, needs a total alkalinity level of between 80 and 120 parts per million (PPM), which can easily be checked by using a test strip.

The sanitiser (chlorine or bromine) you add to your hot tub water won’t act effectively if the TA isn’t in this range. Your hot tub’s water might also become cloudy or foamy.

You can increase TA using an alkalinity increaser, which adds more alkalinity to the water. You’ll bring it down using a pH decreaser, as decreasing the water’s pH will bring the alkalinity down.

The Dangers of Unbalanced Total Alkalinity (TA) Levels:

Persistently High TA levels can cause: ⇪🧪

  • Scaling on the hot tub’s surface and plumbing equipment
  • Poor sanitiser efficiency
  • Lower effectiveness of chlorine, disrupting the hot tub’s disinfecting processes

Persistently Low TA levels can cause: ⇩🧪

  • pH levels to fluctuate excessively
  • Cloudy water to build
  • Irritation to both the eyes and skin

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hot tub chemical guide

As you might remember from school, pH is measured on a scale from 0 (acidic) to 14 (basic), with 7 being neutral.

If your hot tub’s water is too far to either extreme you’ll run into problems, so you’ll need to keep it between 7.2 and 7.6.

You can use a pH increaser or pH decreaser to adjust your hot tub’s pH level to this recommended range.

Because water’s Total Alkalinity affects its pH, you should always adjust your hot tub’s Total Alkalinity first, then its pH after.

The Dangers of Unbalanced pH Levels:

Persistently High pH levels can cause: ⇪🧪

  • Cloudy and foamy water
  • Unwanted build-up of scale
  • Cleaning sanitisers (chlorine or bromine) to become significantly less effective
  • More frequent filter replacements
  • Irritation to both the eyes and skin

Persistently Low pH levels can cause: ⇩🧪

  • Adverse effects on the waters Total Alkalinity
  • Cleaning sanitisers (chlorine or bromine) to become significantly less effective
  • Irritation and dryness of both the eyes and skin
  • Decay and corrosion of your tubs components e.g., the pumps
  • More frequent filter replacements

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Total Hardness

spa chemicals

Total Hardness is the amount of calcium in the water. 

Hard water contains lots of calcium and magnesium, which build up on taps and in pipes and form limescale. Some parts of the UK have hard water, while others have soft water (which is lower in calcium and magnesium and high in sodium).

Hot tub water needs to be on the hard side, or else it will gradually eat away at your hot tub’s shell and components over time.

The ideal Total Hardness in your hot tub is 175-250 PPM, and you can adjust this with a calcium hardness increaser and decreaser.

The Dangers of Unbalanced Total Hardness Levels:

Persistently High Total Hardness levels can cause: ⇪🧪

  • Scale build-up resulting in white deposits that can clog the filters or float in the hot tub
  • Major problems when trying to adjust pH levels
  • Irritation to both the eyes and skin

Persistently Low Total Hardness levels can cause: ⇪🧪

  • Corrosion to the spa’s fittings and parts exposed to the calcium-starved water
  • A lack of sanitiser can lead to algae and bacteria growth
  • Cloudy water to build

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What Hot Tub Chemicals Do You Really Need?

Every hot tub owner needs these chemicals:

  1. Hot tub sanitisers like chlorine or bromine (more on this later).
  2. Alkalinity increaser to raise your hot tub’s Total Alkalinity.
  3. pH increaser and decreaser to control your hot tub’s pH level.
  4. Calcium hardness increaser and decreaser to control your hot tub’s Total Hardness.

Optional chemicals you might also want to pick up include:

  1. Line flush cleaner, which flushes every bit of bacteria out of your hot tub’s pipes.
  2. Filter cleaner, which makes cleaning your hot tub filters a lot easier.
  3. Defoamer, in case you ever need a temporary and short-term fix for hot tub foam.
  4. Hot tub shock, in case you ever need a temporary and short-term fix for cloudy hot tub water.
  5. Hot tub enzymes, which help break down organic contaminants in your hot tub’s water and prevent bacteria from developing.
  6. 303 Aerospace Protectant, which protects your hot tub’s vinyl cover from UV rays, stopping it from fading and cracking.
  7. Water conditioner, which eliminates scum lines, prevents scale build-up, helps maintain proper pH levels, and makes spa water feel soft and silky.

Which Hot Tub Sanitiser is Best?

hot tub chlorine
Kit of Ph chlorine and bromide test. Close-up on the test zone for chlorine and bromide

Sanitiser is a key hot tub chemical, as it keeps your hot tub hygienic and safe to use by killing bacteria.

The two most popular sanitisers are chlorine and bromine. Neither is particularly superior, as they each come with their own set of pros and cons:


Chlorine is most home spa owners’ sanitiser of choice.

Chlorine creates a bacteria-killing acid when it’s added to water. This acid leaves behind chloramines, which causes that swimming pool smell.

To keep your hot tub clean, you need to keep its chlorine levels between 3 and 5mg/l (milligrams per litre). Lower than this and it won’t be effective at killing bacteria. Higher and it can damage your spa’s components and irritate your skin, eyes, and lungs.

Chlorine comes in both granules and tablets. You place chlorine tablets in a floating dispenser and they dissolve gradually over time, while you add chlorine granules directly to your hot tub’s water every time you need to boost its chlorine levels.


Just like chlorine, bromine dissolves in water and kills bacteria.

Bromine isn’t as strong as chlorine, so you need to add more each time you top it up to keep it at 4 and 6 mg/l. But it also acts more slowly, so you don’t need to top it up as often. Plus, it doesn’t create chloramines, so you don’t get that distinctive chlorine smell.

Because it’s a bit kinder on the skin, bromine is a good option if you have sensitive skin.

But it is a bit more expensive and not as readily available as chlorine, which you’ll find in any reputable hot tub dealership across the country.

No matter which kind of sanitiser you go for, be sure to carefully follow the manufacturer’s instructions every time you add it to your hot tub to make sure it works as effectively as possible.

And never use chlorine and bromine at the same time, as this can cause a dangerous reaction. If you want to switch from one sanitiser to the other, drain and deep clean your hot tub to avoid cross-contamination and use the new sanitiser in a fresh batch of hot tub water.

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How Often Should You Add Hot Tub Chemicals?

You should test your hot tub’s pH and sanitiser level with test strips every day that you use it:

  1. Add a pH increaser if your hot tub’s pH is below 7.2 and a pH decreaser if it’s above 7.6.
  2. If you use chlorine to sanitise your hot tub, use a chlorine test strip to check the chlorine level is between 3 and 5mg/l. If it’s below this, top it up.
  3. If you use bromine to sanitise your hot tub, use a bromine test strip to check the bromine level is between 4 and 6mg/l. If it’s below this, top it up.

Every week, you should test the total alkalinity and total hardness:

  1. Add an alkalinity increaser if your hot tub’s TA is below 125 PPM and a pH decreaser if it’s above 155 PPM. Then test the pH and adjust accordingly.
  2. Add a calcium hardness increaser if your TH is below 175 PPM and a calcium hardness decreaser if it’s above 250 PPM.

How to Add Hot Tub Chemicals

chemicals for hot tubs
tester with tablet and powder of chlorine or bromide for maintenance of water quality of hot tub or spa

You will get the best results if you stick to this routine whenever you add chemicals to your hot tub:

First, you need to test your hot tub’s water using test strips or a liquid test kit to see how much the Total Alkalinity, pH level, Total Hardness, and sanitiser level need to be adjusted.

Keep your hot tub running, as this will help mix the chemicals you add in, but make sure you close your hot tub’s air valves so the jets aren’t running too powerfully, as this is likely to cause the chemicals to gas off too quickly.

Grab the chemicals you need to add, then refer to the manufacturers’ instructions to see how much of each you need to add to get your hot tub’s chemistry right.

Precision is key here, so be sure to carefully measure each chemical before adding it rather than eyeballing it, and also aim to spread the chemicals evenly around the water.

Always start by adjusting the Total Alkalinity (if it needs changing). Once you’ve got that dialled in, check the pH level and adjust that if necessary. Then you should test and adjust the Total Hardness and sanitiser levels.

Add your chemicals and leave your hot tub’s jets to circulate them for at least 15 minutes. Leave your hot tub’s cover off here so the chemicals have a chance to off-gas.

Before you get in, test the hot tub chemical levels again to make sure they’re where they need to be, then you can make any further adjustments if necessary.

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Can You Use Your Hot Tub Without Chemicals?

If you don’t take care to balance your hot tub’s chemistry or keep it topped up with sanitizer it will become a breeding ground for bacteria – and certainly not something you’ll want to hop into.

At an absolute minimum, you need to add sanitiser to your hot tub and the chemicals needed to keep its Total Alkalinity, pH level, and Total Hardness in check.

How Soon Can You Use Your Hot Tub After Adding Chemicals?

adding chemicals to hot tub for first time

You need to leave your hot tub sitting with its jets running and the cover off for at least 15 minutes after adding spa chemicals before you use it, to ensure the chemicals completely dissolve.

So, be sure to test your home spa’s water and make any adjustments to its chemistry before you’re planning on hopping in.

How Long Do Hot Tub Chemicals Last?

Hot tub chemicals tend to have a shelf life of several years. Be sure to check the packaging to make sure your chemicals are still in date if you’ve had them for a while though.

How to Use Hot Tub Chemicals Safely

Handling and adding chemicals to your hot tub without proper care can be dangerous and lead to chemical reactions, so be sure to follow these tips to ensure proper safety:

  • Never combine the chemicals needed for your hot tub, e.g., bromine granules with chlorine granules.
  • Always read and adhere to the chemical instructions set out on the label.
  • Test the water in your hot tub every day using the test strips to monitor the levels of any chemicals.
  • Make sure you always add the chemicals to your hot tub water and never the other way around.
  • Never add ANY chemicals to the hot tub water while bathers are inside.
  • Beware of winds and don’t throw chemicals upwards when adding them to the water, keep as close to the water as possible to avoid chemicals becoming airborne.
  • Never let children handle hot tub or swim spa chemicals, keep them out of reach at all times.
  • To avoid irritating your skin, wear protective long-sleeve clothing when handling and applying chemicals to the spa water.
  • If you do get chemicals on your skin, be sure to rinse your skin with clean water straight away.
  • Always wash your hands thoroughly with warm soapy water after handling hot tub sanitiser and chemicals.

When handling any chemical products made for hot tubs, NEVER eat, drink, or smoke while carrying out your maintenance.

If chemicals are ever inhaled or enter your eyes, get plenty of fresh air, rinse your eyes (removing contact lenses if necessary), and sit in a secure outdoor location before assessing how you feel.

If you feel prolonged discomfort in your throat or eyes, do not hesitate to see a doctor and seek medical help.

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How to Store Hot Tub Chemicals

Hot tub chemicals can be extremely dangerous if mishandled, so be sure to keep them tucked away in a cool, dry, and well-ventilated place, well out of reach of children and any animals you may have in the house.

Also, be sure to keep chemicals out of direct sunlight and anywhere that may be humid, as even the slightest humidity and water exposure may lead to dangerous fumes and chemical reactions occurring.

It should also go without saying but refrain from storing chemicals near any sources of direct heat, flammable materials, or diesel/petrol-powered equipment such as cars, lawnmowers, outdoor BBQs or cooking equipment, etc…

You should also make sure the lids for all chemicals are on tight after each use, and be sure to rinse measurement containers out before and after each use.

How to Dispose of Hot Tub Chemicals

Hot tub chemicals could be harmful to the environment, so they need to be disposed of properly.

If you have leftover hot tub chemicals you no longer need, consider giving them to another hot tub owner.

If you can’t find anyone to take your unwanted chemicals off your hands (or they’re out of date), contact your local council for guidance on how to safely dispose of them.

Where is the Best Place to Buy Hot Tub Chemicals?

We advise that you always buy your chemicals and cleaners from a reputable WhatSpa Approved Dealership or the same dealership that you bought your hot tub or swim spa from.

Many top-notch dealerships these days offer repeat chemical subscriptions at a very good value, so you don’t have to worry about going online to re-order chemical products on a regular basis.

The Final Word

So, there you have it: absolutely everything you need to know about hot tub maintenance when it comes to chemicals!

While talk of Total Alkalinity and pH levels might seem daunting at first, all there really is to it is regularly testing your hot tub’s water and adding a few scoops of chemicals if it needs adjusting.

If you ever get stuck, just refer back to this guide to get clear on what you might be missing.

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About the author

Alex Clamp

I am the Content Writer and Marketing Officer at WhatSpa? Magazine. I have worked at WhatSpa? for over 8 years, and I recently graduated with Distinction from Northumbria University with a Master's degree in Occupational and Organizational Psychology. My role at WhatSpa? is to ensure that all hot tub lovers can easily access the highest quality and most up-to-date content, news and information from within the UK wet leisure industry.

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