How to look after your hot tub safely and test the water regularly

All hot tubs require regular maintenance to keep the water clean and safe for bathers. Hot tubs are treated in a similar way to swimming pools. There are some differences however, mainly because there is a smaller volume of water and the water is warm. Because of the heat, the chemical balance can constantly change. Therefore, it is important that the hot tub is monitored regularly so any changes can be detected early and acted upon. Generally, the amount of chemical used is measured in ppm (parts per million) or mg/l (milligrams per litre).

Once you have been testing and adjusting each element in the hot tub for a while, the maintenance will become a lot easier. 

The key chemicals which should be monitored regularly include sanitiser (to kill bacteria keeping the water safe), pH level, alkalinity, total hardness, Total Dissolved Solids (TDS) as well as bacteria.

  • Sanitiser - the main sanitisers used are chlorine or bromine, a choice you need to make is which chemical to use.  In hot tubes, the amount of free chlorine should be 3-5ppm and bromine 4-6ppm.
  • pH* level -  the ideal pH for a hot tub is 7.2 – 7.6 (for chlorine users) and 7.0 – 7.4 (for bromine users). If the pH is outside this level (either too acidic or too alkaline) this can have a negative effect, therefore it is important to test the pH level regularly. If your hot tub is too acidic, the sanitiser is less effective and can cause irritation to eyes but also damage parts of the hot tub. If the pH is too high (alkaline) again the sanitiser can be less effective, the water can become cloudy and scale builds up. Once the current pH level has been tested, a pH decreaser or increaser can be used to change the pH levels.
  • Alkalinity** - before you can start looking at pH levels, it is important to balance the alkalinity as it acts as a buffer and gives you the ability to better control the pH level of your hot tub. Alkalinity should be between 80 and 120ppm (anything above or below that will make it harder to adjust the pH level). Make sure to check the alkalinity again once the pH level has been adjusted, as the alkalinity might have been changed.
  • Total Hardness - measures the levels of dissolved minerals, most commonly this is calcium and magnesium. The ideal hardness reading is 100 – 250ppm. Too hard and there will be scale and cloudy water. Too low and it will force the water to draw from other minerals such as aluminium, copper and iron which can damage the parts of your hot tub that are built from these materials.
  • Total Dissolved Solids (TDS): over time, minerals, chemicals and other soluble materials will lead to an increase of TDS. This can reduce the effectiveness of chemicals, cause dull water and making it harder to maintain. Therefore, a monthly change of water is recommended. Test for TDS at least once a month (depending on use etc)
  • Bacteria - can grow within the hot tub, therefore it is recommended to check the level of bacteria regularly. Specially designed bacteria test strips for pool & spa detect E.coli, Pseudomonas and many other forms of bacteria in water and provide results within 15 minutes.
  • Visually also check
    • for foam, which can be caused by remnants of detergents left in bathing costumes, and
    • check the filtration system is in good working order.
pH is a scale of 0 to 14* and is used to measure how acid or alkaline a liquid is. A pH below 7 is acid, 7 is neutral and above 7 is alkaline. Very acidic water can destroy a hot tub and its working parts, but also irritate skin and eyes. Very alkaline water prevents the chemicals from doing their job of keeping the water clean, dry the skin, affect swim wear and make eyes red and itchy.
About alkalinity** If the alkalinity of your hot tub is too low, then the pH is unstable and can change easily. If the alkalinity is too high, then the pH will go up and make water cloudy and create scale on the surface of the hot tub. So before adjusting the pH level, check the alkalinity level and potentially change it.

How to test hot tub water

1) Using test strips

Testing the water is key to keeping the water safe, clean and healthy. The easiest and most cost-efficient way to test is using test strips which indicate chlorine/bromine, pH, alkalinity & hardness quickly and accurately. Appropriate chemical adjustments can be made once the water has been tested.

To test, simply put your test strip into the water, hold it about 15cm under water, then take it out. Wait as instructed and then compare the colour change with the closest colour on the colour chart. Each pack of test strips comes with detailed instructions and a colour chart on the pack. If your tested elements are not within the required range, then you can adjust them.

Specialist strips for people who use other sanitisers:

To view the full range of our pool & spa testing products, click here.

2) Using a photometer

The eXact photometer for Spas delivers labquality results when testing for 7 important spa parameters: free chlorine, total bromine, combined/total chlorine, pH, total alkalinity, calcium hardness. All tests have been specifically calibrated for spa temperatures and use reagent test strips for quick and reliable analysis. It is available in two options as a meter only or as a complete starter pack (meter and reagents).

To view the full range of pool and spa photometers, including our complete starter packs, click here.

How often to test hot tub water

A hot tub should be tested at least once a week to ensure that the chemicals you add are at the right levels. It also helps to keep it clean and prolongs the life of the hot tub. Heavy use requires testing more often.

General Hot Tub safety tips

For any hot tub owner / user it is important to keep our safety tips in mind at all times:

  • Do not allow hot tub temperatures to exceed 40℃ (lower if children will be using the hot tub)
  • Shower before you get in
  • Keep the lid on when not in use, it ensures nothing falling in
  • Regularly replace the water before it gets cloudy and a film builds up on the surface*** , this is also a good opportunity to give the hot tub a good clean
  • Never leave non-swimmers / children unattended in a hot tub
  • Do not overload your Spa with more people than its recommended size
  • Do not use electrical appliances near your hot tub
  • Do not use glass around or in a Spa
  • Do not drink alcoholic beverages before or while using a hot tub
  • Clean the hot tub (don’t just rely on sanitiser) by wiping down the interior surface with an unbleached cloth or sponge
  • Clean the filters regularly
  • If you’re pregnant, have high blood pressure or any cardiovascular conditions please contact your doctor before using a hot tub
  • Always wear gloves when cleaning / changing hot tub filter cartridges

*** How to know when to do that: Take the number of gallons of your hot tub holds when it’s full. Divide that number by the number of people who regularly use the hot tub. Then divide that number by three. This will tell you how often you should change the water. For example, a Coleman Lay Z Spa holds 254 gallons.  If 2 people regularly use the hot tub, then 254 divided by 2 gives you 127. Now divide 127 by 3, and you get 42.  That means you’ll need to replace the water every 42 days.

 

 

Further Free Resources:

Got a question about water testing? Try our complete list of Free Water Testing Resources. Here are the most frequently read guides:

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Disclaimer: Only opinions based upon our own personal experience or information detailed in academic journals or other publications is cited. This has been done exclusively for anyone who is interested in this subject but is not intended to replace proper analysis. We cannot accept responsibility and liability of any kind which may result from the application of this information. We always recommend to consult an expert to discuss any test results or get a full recommendation on the specific subject and specific to your situation by an expert.

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There are strict standards for the quality of drinking & bathing water within Europe mainly laid down in the EU Drinking Water Directive (98/83/EC). These are based on advice from the World Health Organisation (WHO).