How to Balance Hot Tub pH and Total Alkalinity
Keep pH between 7.0 and 7.8, and balance total alkalinity to hold it there
pH shows how acidic or alkaline the water is, and it moves with use, rain and fresh water. Total alkalinity works alongside it. This guide shows how to test both, and how to adjust them with the right product.
Test, adjust one thing at a time, wait, then test again.
What pH and total alkalinity do
pH tells you how acidic or alkaline the water is. The CDC gives 7.0 to 7.8 as the range for hot tub water, and advises testing pH and sanitiser levels at least twice a day.1
Our pH products are labelled for 7.2 to 7.8, so that is the band to aim for when you use them.2
Total alkalinity works alongside pH. Our alkalinity increaser page says balanced total alkalinity helps control the pH level, so check the two together.4
How to test
Test pH and total alkalinity together
Our 3-in-1 test strips read free chlorine or bromine, pH and total alkalinity in one dip, so you can check all of them at once. See the strips.1
Use tablets for a second pH reading
Phenol red rapid tablets check pH on its own, and work with a colour comparison kit. See the tablets.
Test before you bathe
Test pH and sanitiser levels at least twice a day, and more often when the tub is in heavy use.1
How to adjust pH
Change one thing at a time, with the pumps running, and retest after each change.
Lower pH if it is above 7.8
Use pH minus. Dissolve it in warm water in a clean plastic container, up to 10 g per litre, stir until fully dissolved, then add it to the tub with the pumps on.2
Raise pH if it is below 7.2
Use pH plus, dissolved and added the same way.3
Wait, then retest
Wait at least 30 minutes, then test again. Repeat until pH is between 7.2 and 7.8.2
Wait before bathing
Wait at least 2 hours after adding a pH product before you bathe.2
How to adjust total alkalinity
Our alkalinity increaser page aims for 80 to 120 ppm.4 A public health guide from King County, Washington gives 80 to 125 ppm for wood, plaster or tile tubs, and 125 to 150 ppm for vinyl, painted or fibreglass tubs.5 Check your tub's manual for its recommended figure.
Clear the tub
Make sure bathers are out of the tub before you add anything.
Add the alkalinity increaser
Add it at the dose on the pack, with the pumps on so it circulates evenly.4
Wait 10 minutes, then retest
Leave for 10 minutes, retest, and raise in steps of 10 ppm until the reading is in range.4
Wait before bathing
Wait at least 2 hours after using the increaser before you bathe.4
Target numbers
| Check | Aim for | How often |
|---|---|---|
| pH | 7.0 to 7.8 (CDC range). Our pH products are labelled for 7.2 to 7.8.12 | At least twice a day1 |
| Total alkalinity | 80 to 120 ppm on our alkalinity increaser page.4 King County: 80 to 125 ppm for wood, plaster or tile; 125 to 150 ppm for vinyl, painted or fibreglass.5 | With each pH test |
| After adding a pH or alkalinity product | Wait at least 2 hours before bathing24 | Each time you add one |
The products
Every product here is a current Outdoor Living product, in stock now.
1.5 kg · from £8.49
Lowers pH when it is above 7.8. Dissolve it first and add it with the pumps on.
1 kg · £7.99
Raises pH when it is below 7.2. Follow the same dissolve and add steps.
Hot Tub Total Alkalinity Increaser
1 kg · £7.99
Raises total alkalinity to the range above, in steps of 10 ppm.
3-in-1 Pool and Hot Tub Test Strips
Pack of 50 · £4.99
Checks free chlorine or bromine, pH and total alkalinity in one dip.
Quick answers
Open a question to read the answer.
What pH should my hot tub be?
Between 7.0 and 7.8, according to the CDC. Our pH products are labelled for 7.2 to 7.8.
What happens if the pH is too high?
Above 7.8, the water can become dull, scale can form, and sanitiser may not dissolve as well.
What happens if the pH is too low?
Below 7.2, the water can cause itchiness and eye burn, and the sanitiser works less well.
How long after adding pH products can I bathe?
Wait at least 2 hours after adding a pH or alkalinity product before you bathe.
What total alkalinity should my hot tub have?
Our alkalinity increaser page aims for 80 to 120 ppm. King County gives 80 to 125 ppm for wood, plaster or tile tubs, and 125 to 150 ppm for vinyl, painted or fibreglass tubs.
Sources
- Centers for Disease Control and Prevention, Operating and Managing Public Pools, Hot Tubs and Splash Pads (dated 10 January 2025): pH 7.0 to 7.8, testing at least twice a day, shock daily to weekly
- Outdoor Living, Hot Tub pH- Reducer product page: pH range, dosing and wait times (current)
- Outdoor Living, Hot Tub pH+ Increaser product page: pH range, dosing and wait times (current)
- Outdoor Living, Hot Tub Total Alkalinity Increaser product page: target range, dosing and wait times (current)
- King County, Washington, Department of Public Health, Staying Happy and Healthy in Your Spa and Hot Tub, sixth edition (undated): total alkalinity ranges by tub material
Paul Margerison
Managing Director & Founder, Outdoor Living
Clear water is a routine, not a one-off job. Testing pH and total alkalinity together, at least twice a day, is the habit that keeps it steady.