How to read hot tub test strips

What the pads measure

Most hot tub strips have three to five pads. The usual ones are free chlorine or bromine, pH and total alkalinity. Some add total chlorine, total hardness or cyanuric acid. Check the pot to see which pad is which, as the order varies between brands.

Use strips made for your sanitiser. A chlorine strip will not read bromine correctly, and some strips read both on one pad with two charts. The chart on the pot also gives the ideal range for each pad, usually shaded.

How to take a reading

Read all pads within the time given. Colours keep developing, so a pad read too late can look higher than it is.

1. 1

   Run the filter pump for a few minutes so the water is mixed.

2. 2

   Take one strip out with dry fingers and close the pot straight away.

3. 3

   Dip the strip about elbow deep, away from the pump outlet, for the time on the pot.

4. 4

   Remove it and hold it level. Do not shake hard; a gentle flick removes excess water.

5. 5

   Wait the time stated on the pot, often around 15 seconds.

6. 6

   Compare each pad with the chart in daylight, not under coloured lights.

7. 7

   Note the readings before they change colour further.

Matching colours accurately

Hold the strip right next to the chart, not on top of it, and match each pad to the nearest block. If a pad sits between two blocks, take the value in between. Daylight is best; indoor bulbs, LED lights on the tub and sunglasses all change how colours look.

If readings look odd, check the date on the pot. Strips lose accuracy when old or damp, so keep the lid tight and store them indoors. If in doubt, test again with a fresh strip, or check with a liquid test kit.

The order to correct readings

After each adjustment, run the pump, wait the time on the label and test again before the next step. Dose from your tub's litres and follow the chemical maker's instructions. See pH and alkalinity for which product moves which reading.

How often to test

In summer, when the tub is warm and in regular use, test before each use or at least three times a week. Heat, sunlight and bathers use up sanitiser faster. In winter or with light use, a couple of times a week is usually enough, plus a test after any heavy session or after rain gets in.

Always test after filling, after a shock treatment before getting back in and if the water looks cloudy, smells strong or feels different.

• After filling: test and balance before first use.
• Busy weeks: test before each use.
• Quiet weeks: test two or three times a week.
• After shock: test sanitiser before use.
• Anything odd: test straight away.

When readings will not settle

If readings keep drifting after you correct them, check the filter, shock the water and make sure sanitiser is topped up after use. Water that has been in the tub for a long time collects dissolved solids that make balancing harder; a drain, clean and refill is often quicker. See how to drain an inflatable hot tub.

Note:Store test strips and chemicals out of reach of children, and follow the instructions on each product.

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Frequently asked questions

How long do you leave a test strip in a hot tub? Usually a second or two. Check the pot, as times vary.

Why do my strips show different readings each time? Old or damp strips, reading too late or poor light are common causes. Use fresh strips and read within the time given.

Can I use pool test strips in a hot tub? Use strips with ranges suited to hot tubs and to your sanitiser.

Do Lay-Z-Spa test strips work in other tubs? Hot tub strips generally measure the same things. Check the pads match your sanitiser.