How to test water in hot tubs

Monitoring the water in your hot tub is key to making sure it is safe for day-to-day use. Using a hot tub tester or meter is an easy way to keep on top of your water chemistry for health and safety as well as bather comfort, providing peace of mind and ensuring you can comply with any health and safety requirements. 

Read on now to learn more about how to test the water in your hot tub with a digital meter:

Why do you need to test the water in hot tubs?

Hot tubs require sanitation to be safe for use, whether you have a personal tub or you offer hot tubs to guests as a holiday park, Airbnb host or hotel that needs to comply with HSG282 legislation. Chlorine is the most common choice of sanitising agent for hot tubs and swimming pools, providing an effective way to keep the water clean with regular use. 

To maintain the specific level of sanitation from chlorine, both pH and chlorine levels need to be monitored daily or weekly, depending on usage. These two parameters in tandem are key to maintaining safe levels of hygiene in the water. Other parameters should also be tested to maintain your hot tub and preserve its life, which we cover in detail below.

What happens if you don’t monitor your hot tub water?

If your sanitation level is too low, this can allow bacteria and pathogens to grow in the water, which increases the risk of illnesses such as Legionnaires’ disease or E. coli. If your hot tub water chemistry is too strong, this can cause skin and eye irritation, making the water unpleasant for bathers.

Fixtures such as heaters, jets and pipework can also be damaged by unbalanced water chemistry due to scaling or corrosion. Using accurate digital testers for hot tubs is the best way to keep your water in the best condition for the experience of bathers and the lifetime of the tub itself.

Steps for testing hot tub water

Using a digital meter or tester for measuring hot tub water is a quick and easy way to track all important parameters. Here are the steps for testing with the different types of electronic meters available for hot tubs:

Testing with a digital tester

A digital pH tester for hot tubs like the HI-981074 handheld meter is a simple and cost-effective way to quickly measure pH in your hot tub. The steps for using this type of digital meter are as follows:

1. Turn the tester on and dip it directly into the hot tub water
2. Wait for the reading to stabilise
3. Record your reading and make adjustments as necessary

Testing with a photometer

A multiparameter meter like the HI-971044 photometer allows you to measure all the important parameters in your hot tub, including chlorine, pH and cyanuric acid. The steps for using a hot tub photometer are as follows:

1. Take a sample of water from the middle of the hot tub with the vial
2. Add any required reagents into the vial
3. Insert the vial into the photometer
4. Press the READ button to test and make any necessary adjustments

Testing with a hot tub controller

Automating your hot tub water dosing with a cloud-connected controller like the BL-132-20 means you don’t have to test manually, and the dosing process is completed for you, reducing day-to-day hot tub water maintenance. To view the automatically logged tests, the steps are as follows:

1. Connect to the Hanna Lab app
2. View all logged readings of pH and chlorine
3. Make any adjustments to the proportional band or flow as required

It’s important to note that temperature affects the readings of pH in water. For the most accurate reading, you should test at the temperature the hot tub runs at when it is active. If there are visual changes in the water, such as cloudiness, this is a good indicator that you should test all important parameters before bathers are allowed in the water. 

What should you test for in hot tubs?

pH

pH measures how acidic or alkaline the water is. This parameter should always be the first step in hot tub testing, as it has a direct impact on sanitation. Ensuring the pH is in the correct range and making adjustments ahead of adding other chemicals can help reduce the cost of chlorine additives. The optimal pH range for hot tubs is around 7.2 to 7.6 pH.

Chlorine

Chlorine is a common sanitiser for hot tubs. This chemical eliminates pathogens, bacteria and contaminants in the water, making the tub safe for use. Testing the chlorine in hot tubs after you have tested the pH is the ideal way to stay within the suitable range for private and public use, meeting health and safety standards. The ideal range for chlorine is roughly 3 to 5mg/L.

Total alkalinity

Alkalinity acts as a buffer in hot tub water, preventing pH levels from swinging significantly and impacting the effect of sanitation. Regularly testing the total alkalinity of the hot tub water provides vital information to maintain balance and can prevent damage from scaling and corrosion due to variable pH. You want your total alkalinity to be around 80 to 120mg/L CaCO3 to be effective.

Cyanuric acid

Stabilised chlorine tablets often include cyanuric acid, a chemical that helps to prevent chlorine from degrading due to ultraviolet rays from the sun. While this chemical is important, too much of it can lead to over-stabilisation, which requires a full drain. Testing regularly ensures your chlorine is still in the effective range. Below 70 mg/l of cyanuric acid is typically considered the right level to prevent stability while providing protection.

Other parameters to consider

• Calcium hardness: Also known as total hardness, measuring calcium hardness can provide insight to reduce calcium in the water to help to prevent significant scaling of the heaters and jets in hot tubs.
• Phosphate: A high level of this parameter can lead to algae blooms, turning the water green. Monitoring with a digital Checker for phosphate can provide the information to keep this parameter to a minimum.

Testing for swimming pools

If you need to test the water in a swimming pool, many of the same requirements of measurement apply. Hanna’s Pool Line range of testers, photometers and controllers are suitable for hot tubs, pools and spas, providing an easy way to monitor multiple facilities with digital instrumentation. Learn more in our complete guide to pool water testing here.

Buy hot tub testing meters from Hanna

Hanna’s Pool Line series includes a wide selection of easy-to-use digital testers for hot tubs and pools. From simple dip-and-test water meters to fully automated controller systems, our range includes everything you need to accurately monitor the water in hot tubs. Shop Pool Line online now.

Have questions for the experts? Contact our pool ambassadors directly to get a personalised recommendation by calling us on 01525 850 855 or emailing our team at sales@hannainstruments.co.uk.