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Hot Tub & Spa Chemicals Guide

Updated: Feb 1, 2019

When it comes to either owning a hot tub or renting a hot tub, it is important to understand how different chemicals can affect the water. We've created a simple but brief guide to explain how to use and get the most from your hot tub chemicals.

The first thing that you need know is that your hot tub is not a tiny pool. Hot tub water - its treatment and parameters - is much different than a swimming pool. The main difference of course, is the temperature – Hot tub water is most often set between 37.5°C and 40°C, while a pool stands typically between 25°C and 28°C, which also means that there's far more opportunity for bacteria growth in a hot tub.

Hot tub chemistry

As hot tub water is warm, its chemical balance is constantly changing and the measured application of water balance chemicals will keep your hot tub water clean and free from harmful bacteria for longer. That is why hot tub owners must ensure they monitor for any changes in the chemical balance of the water and act appropriately.

Most common questions we’re asked about hot tub and spa chemicals are:

What is a hot tub sanitiser?

A sanitiser is a disinfectant chemical used to kill bacteria and purifies the hot tub water. The sanitiser is the most critical component to a healthy hot tub experience.

There are two popular sanitisers used to protect the water within hot tubs, which are chlorine (the stronger of the two) and bromine and are available as granules & tablets.

If you’re a hot tub owner with sensitive skin, then the use of bromine or even oxygen, a less popular sanitiser, are recommended.

Other products that do help destroy micro-organisms but are not effective enough to use alone are Secondary Sanitisers which are;

  • UV (ultra violet) is not a primary sanitiser.

  • Ozonators are not primary sanitisers.

  • Oxidisers aka non-chlorine shock or MPS are not primary sanitisers.

UV, Ozone and oxidisers can be noted as chemical reducing aids, but still require the use of a halogen based or primary sanitiser.

For more detailed information about sanitisers, we have a chlorine guide, a bromine guide and an oxygen guide available. Please Contact Penguin Hot Tubs and Swim Spas directly on 0800 112 3886 or email


What is PPM?

PPM is an abbreviation for "parts per million" and it also can be expressed as milligrams per litre (mg/L). This measurement is the mass of a chemical per unit volume of water.

In hot tubs it is essential to keep the amount of Chlorine at between 3-5 ppm.


What is pH?

pH > potential Hydrogen. You might remember acids and bases from your school chemistry class. When a solution (that’s a chemical mixed with water) contains extra hydrogen ions, it’s acidic. When the solution has fewer hydrogen ions than plain water, it’s basic.

Some consider this the most important component of water balance. It measures how acidic or basic your water is. If it is not kept in check you run the risk of damaging your equipment, i.e. heating elements and pump seals.

The pH scale works from 0-14 with 7 being neutral, anything below 7 is classed as acidic while anything above 7 is considered an alkaline.

For hot tubs, the term pH is a scientific way of describing whether your water is acidic or alkaline with the ideal pH for hot tub water is between 7.2 - 7.6 parts per million (ppm) – as close to neutral 7 as possible.

If your hot tub pH measures outside that neutral range, you could be in for some unhealthy and potentially damaging water symptoms in your hot tub, such as bacteria growth or corrosion.

Listed are the most common problems associated with both low or high pH levels:

Low pH

  • Poor sanitiser efficiency

  • Corrosion of metal parts (heaters, steps, other equipment)

  • Eroding of the pool plaster or grouting

  • Staining of the hot tub surface

  • Burning eyes/nose

  • Itchy skin

  • Destruction of Total Alkalinity (TA)

  • Fading of swimwear, pool toys, etc.

High pH

  • Poor sanitiser efficiency - leading to algae growth

  • Scale or calcium formation

  • The need for frequent filter cleaning due to filter clogging

  • Burning eyes/nose

  • Itchy skin

  • Dull or cloudy water

We sell all the chemicals you would need to help balance your hot tubs pH levels.

Want to know more? Read our guide - How to balance your hot tub pH level. Please Contact Penguin Hot Tubs and Swim Spas directly on 0800 112 3886 or email


What is Total Alkalinity?

Total alkalinity (TA) - is the measure of all the alkaline material in the water, and in essence, lets us know the water's ability to resist changes in pH. We find a lot of people confuse a hot tubs pH level and the total alkalinity. Alkalinity refers to the amount of alkaline salt affecting the balance of your hot tub water, which will also affect the water hardness.

TA acts as a buffer for the pH level in your water, keeping the pH level stable while allowing you to adjust TA without throwing the rest of your hot tub chemistry into chaos.

Total alkalinity is so important to your water balance, the first step in your water care process will always be measuring and adjusting TA before any other chemicals. The ideal range for TA is between 80-150 ppm (parts per million).

When you adjust your alkalinity, add small doses, one at a time. Allow the dose to circulate before testing again. Only after your TA is in the optimal range should you move on to adjusting pH. Achieving the right TA may actually get your pH in the target range.

Listed are the most common problems associated with both low or high total Alkalinity levels:

Low total Alkalinity

  • Corrosion of metal parts (hearters, steps, other equipment)

  • Staining of the hot tub shell

  • Rapid fluctuations in pH

  • Burning eyes/nose

  • Itchy skin

  • Green water

High total Alkalinity

  • Poor sanitiser efficiency - leading to algae growth

  • Stagnant pH levels

  • Scale or calcium formation

  • Burning eyes/nose

  • Itchy skin

  • Cloudy water

We sell a full range of chemicals you would need to help increase the total alkalinity balance. Want to know more? Read our guide - How to balance your hot tub pH level orcontact Penguin Hot Tubs and Swim Spas directly on 0800 112 3886 or email


What is Total Hardness? (TH)

Sometimes referred to as "Calcium Hardness", total hardness is a measurement of minerals in your water including calcium and magnesium. You do want your water to have some level of hardness. If the water does not have enough calcium, the water will draw from other minerals, including copper, aluminium and iron, (e.g., heating elements, pump and seals). This will result in equipment corrosion. If there is too much hardness, you will see scale formation on the hot tubs interior and the water will take on a cloudy appearance. Because of this, it is recommended that you fill your hot tub with water from a softener instead of tap water – see chart above. You should ensure your hot tubs calcium reading is between 100-250 PPM. If the levels of calcium hardness in your water are above this, we advise using a no scale product which is designed to keep calcium from solidifying on the shell and internal hot tub parts.


What is hot tub shock?

Shocking your hot tub is the easiest way you can ensure that the water is safe and free from all contaminant. Whenever you open your hot tub, or after a period of inactivity or even heavy use, it is a good idea to shock it before you begin using it.

Why Shock Your Hot Tub?

The most obvious reason for shocking your hot tub is to clean the water so it is safe for soaking. If your water is cloudy, shock may take care of that as well. But what does shock really do for your water?

There are four main reasons to shock your hot tub:

  1. Remove organic compounds from the water. If you use your hot tub often or you have 3 or 4 bathers in there at once, the level of organic compounds can spike quickly. Removing these compounds is a must for clean water.

  2. Kill bacteria. Chlorine and bromine-based shock compounds can easily kill bacteria growing in the water, so it is safe. However, if you use other types of shock compounds, they will not disinfect the water.

  3. Remove bromamines or chloramines from the hot tub. Adding shock once a week will help break the bonds that form these contaminants so they can easily be removed from the water.

  4. Reactivate bromides in the spa. If your hot tub uses bromine, adding shock once a week will help activate it to properly clean the water of your hot tub.

There are two main types of shock compounds available today – chlorine shock and non-chlorine shock. Both offer their own strengths and weaknesses and should be a part of every hot tub owners maintenance schedule. If you need more detailed information, read our guide – How to shock your hot tub.


Hot Tub chemical safety

Below are some important tips when using Hot Tub chemicals:

  • Always read the label of any hot tub chemical before use and follow the instructions carefully

  • Never mix hot tub chemicals unless instructed to do so by a specialist

  • Always pre- dissolve any granules in a jug or container before adding them into your hot tub

  • Always add chemicals to water, never the other way around

  • Never add chemicals to your hot tub water while it is in use

  • Only use hot tub chemicals in well ventilated areas

  • Beware of strong winds when using powdered chemicals

  • Always keep all hot tub chemicals out of reach of children and animals

  • Make sure you wash your hands after using hot tub chemicals

  • Penguin Hot Tubs strongly advises wearing protective clothing whenever handling chemicals

  • Test your hot tub water daily (with either Bromine or Chlorine test strips)

  • Store hot tub chemicals away from heat and moisture

  • Always leave your hot tub switched on (unless changing the filter or the water)

Need further advice or assistance? Advice and troubleshooting information can be found here to help you enjoy your hot tub as long as possible or if you can’t find what you are looking for, please contact our hot tub experts directly on 0800 112 3886 or email

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