How to read a hot tub test strip

Posted by Nick Clamp in Maintaining a Hot Tub Guides on 4th January 2022

Testing your hot tub water regularly is a critical part of maintaining the optimal chemical balance. Test strips instantly reveal whether your hot tub chemicals need adjusting.

And using them couldn’t be easier when you know how.

Read on to how to read a hot tub test strip – and what to do once you’ve got your reading.

Are all hot tub test strips the same?

Even the most basic pool and hot tub test strips measure your spa’s Total Alkalinity (TA) and pH levels.

Others measure up to seven elements, including cyanuric acid and nitrite.

An important difference to look out for is which sanitiser a test strip measures: chlorine, bromine, or both. Be sure to get test strips that measure the sanitiser you use.

What kind of test strips do I need for a hot tub?

The three things you must keep on top of to make sure your hot tub stays clean and hygienic are the sanitiser levels (either chlorine or bromine, depending on what you use), Total Alkalinity, and pH.

We strongly recommend you get spa test strips that measure at least these three elements.

Your spa’s Total Hardness (TH) is also well worth keeping an eye on, so we recommend you pick up test strips that measure that as well if you can. 

How do you read a water test strip for a hot tub?

To read a spa test strip, just hold it up to the colour chart on its bottle and match it up to the right colours:

Start with Total Alkalinity (TA), as if this isn’t balanced then your hot tub’s pH levels won’t stay stable and are liable to swing dramatically. Your hot tub’s Total Alkalinity needs to be between 125 and 155 parts per-million (this range will be marked on your test strip’s colour chart).

If you haven’t adjusted your hot tub’s TA, you can move straight on to measuring its pH with the same test strip. This should be between 7.2 and 7.6, which will be the ‘OK’ range on your colour chart.

Keep in mind that adjusting your spa’s Total Alkalinity will affect its pH levels. So, you’ll need to test your spa again with a fresh strip to get an accurate pH reading if you’ve changed its TA.

Next, measure the Total Hardness, which should be between 175-250 PPM, and adjust if necessary.

Finally, measure your spa’s sanitiser levels and top them up if needed. Chlorine levels should be between 3 and 5mg/l, while bromine should be between 4 and 6mg/l.

Not sure of the best way to balance your spa’s chemicals if they’re too high or low? Check out our complete guide to hot tub chemicals here for everything you need to know about hot tub chemistry.

How do you use hot tub test strips correctly?

Follow this simple step-by-step process to make sure you get an accurate reading every time you test your hot tub: 

  1. Spa test strips actually have an expiry date. So, be sure to check the use-by date on their packaging before you use them. 
  2. Turn off all your hot tub’s jets and pumps so the water is still.
  3. Dip the test strip into the water until your wrist is underwater and swirl it around three times to get an accurate reading (most of the impurities in your spa’s water rise to its surface). 
  4. Remove the strip from the water after a few seconds and give it a quick shake so excess water doesn’t mix the colours together.
  5. Hold the strip up to the colour chart on its bottle and match it to the right colours within 30 seconds of removing it from your hot tub to get an accurate reading:
    1. Check the Total Alkalinity first. If this is within the right range, use the reading from the same strip to measure the other elements. If not, adjust the TA then use a fresh strip to test the water again.
    2. Check and adjust the pH level next, then the Total Hardness.
    3. Finally, check the sanitiser level and top it up if needed. 

Can I use chlorine test strips to test for bromine?

Chlorine and bromine are different chemicals, so you can’t test bromine levels with a strip that only measures chlorine.

Make sure you pick up test strips that specifically measure bromine levels if that’s your sanitiser of choice.

How often should I use a hot tub test strip?

You should use a test strip to check your hot tub’s pH and sanitiser level every day and its Total Alkalinity and Total Hardness once a week.

How to store hot tub test strips

It’s crucial you don’t get your test strips wet before you use them.

So, make sure your hands are dry each time you reach into the bottle. Fasten the lid tight every time you close it and you keep it in a cool, dry place too.

Summing up

Reading a hot tub test strip might seem daunting before you’ve given it a go, but it’s as simple as matching the tabs up to the colour chart on the bottle.

Do this every day to ensure your hot tub’s chemicals are always properly balanced, which will prevent all kinds of water quality problems.

About the author

Nick Clamp

I am the Editor-in-Chief at WhatSpa? Media Group and my job is to keep you informed about the very latest hot tubs on the UK market... the best job in the world! When I'm not being deluged with press releases and hot tub brochures I enjoy keeping fit and participating in endurance events including triathlons and distance running.

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