Hot tub pH and alkalinity: target ranges

What pH means

pH is a scale from 0 to 14 that shows how acidic or basic water is. 7 is neutral. Hot tub water is usually kept slightly above neutral. When pH is too high, chlorine and bromine work less effectively, water can turn cloudy and limescale builds up on the heater. When it is too low, the water may feel harsh and can corrode metal parts and stress the liner.

Several things push pH up or down: fresh fill water, sanitiser type, the air bubbles, bathers and rain. That is why it needs checking a few times a week.

What total alkalinity means

Total alkalinity measures the dissolved substances that resist changes in pH, mostly bicarbonates. Think of it as a buffer or shock absorber. If alkalinity is too low, pH swings up and down with every dose. If it is too high, pH tends to creep up and is hard to bring down.

Because alkalinity controls how pH behaves, adjust alkalinity first, wait the time on the label, retest and then adjust pH.

Reference table of target ranges

These are commonly quoted ranges for hot tubs, given as general guidance. Your test kit and chemical labels take priority.

How to adjust step by step

Dose in small steps. It is easy to overshoot, and a second small dose is better than correcting a large one. Use your tub's litres from the manual or the water volume calculator to work out doses.

1. 1

   Run the filter pump so the water circulates.

2. 2

   Test with a fresh strip and note each reading.

3. 3

   If alkalinity is out of range, dose the correct product for your water volume.

4. 4

   Wait the time on the label, usually with the pump running, then retest.

5. 5

   Adjust pH if it is still out of range.

6. 6

   Check sanitiser last and adjust it.

7. 7

   Retest before anyone gets in.

Common problems

In hard water areas, high calcium can push scale onto the heater. See hard water and limescale for general guidance.

• pH keeps rising: check alkalinity is not too high, and remember bubbles push pH up.
• pH will not hold: alkalinity is probably low; raise it first.
• Readings swing after every use: test more often and keep sanitiser topped up.
• Cloudy water with good readings: check the filter and shock the water; see cloudy water.

Safety with chemicals

pH reducers are acidic and pH increasers are alkaline. Handle them with care, add them to water and never to each other, and keep them apart in storage.

Note:Never mix chemicals. Wear gloves and eye protection if the label advises it, store products out of reach of children and always follow the chemical maker's instructions.

How often to test

When the tub is in regular use, test before each soak, or at least three times a week. In cooler months with lighter use, a couple of times a week is usually enough, but always test after heavy use, after rain gets in or after adding fresh water. pH and alkalinity change more slowly than sanitiser, so most of the time you will only need small corrections.

Keep a simple note of readings and doses. Over a few weeks you will see how your fill water behaves, which makes it easier to dose correctly after each refill. Fresh test strips matter too: keep the pot sealed and dry, and replace it once it passes the date on the label.

Frequently asked questions

What should hot tub pH be? Commonly around 7.2 to 7.6. Use the range on your test kit.

Should I adjust pH or alkalinity first? Alkalinity first, because it steadies pH.

Why is my Lay-Z-Spa alkalinity low after filling? Fill water varies by area. Raise it with an alkalinity increaser as the label directs.

Can high pH damage my tub? High pH encourages scale on the heater and reduces sanitiser performance, so keep it in range.