How do I use pool test strips properly?

Why test strips are worth the 60 seconds

Clear-looking water can still be out of balance. A quick strip test tells you whether your chlorine is strong enough to keep bathers safe and whether your pH and alkalinity are where they should be, so the chemicals you add actually work.

The Deep Blue 6-in-1 strip checks free chlorine, total chlorine, pH, total alkalinity, total hardness and cyanuric acid (stabiliser) in one go. Test a pool two or three times a week in the swimming season, and a hot tub before each use or at least twice a week.

The routine, step by step

Timing matters - the colours keep changing if you leave the strip too long, so have everything ready before you start.

• Run the pump for at least 30 minutes first so the water is well mixed.
• Take the sample from about elbow depth, away from the skimmer, returns and any chlorine floater or tablets.
• Take out one strip with dry fingers and close the tub straight away - damp air spoils the strips left inside.
• Dip the strip in the water for 2 seconds, then remove it. Do not swish it about.
• Hold it flat, pads facing up, and give it one gentle flick to shake off the excess water.
• Wait 30 seconds, then compare the pads with the colour chart on the pack, or photograph it with the app.
• Read or photograph it on plain white paper in daylight, out of direct sun. Indoor lighting makes colours look warmer than they are.

Using the app for a more accurate reading

Matching colours by eye is harder than it sounds, especially the pinks and purples of the pH and hardness pads. The app's guided camera shows you where to line the strip up and checks the photo is sharp and evenly lit before it reads it.

For the best accuracy, include the colour chart on your pack - box, bottle or pouch - in the photo when the app asks. The app uses the printed chart to correct for the colour of your light and your phone's camera, which is far more reliable than guessing.

Photos are analysed on your phone - they are not uploaded. You get a clear result for each test, what it means for your pool or hot tub, and a step-by-step plan to put anything right.

New strips from September 2026

Deep Blue 6-in-1 strips made from September 2026 have the pads in a new order, with the pH pad at the tip. Older strips have free chlorine at the tip. Always compare with the chart on the tub the strip came from, as the colours differ between the two.

You do not need to tell the app which strip you have: it detects old and new strips automatically. If it ever looks unsure, it will ask you to confirm.

Getting reliable results

Most odd readings come down to how the strips are stored or read, not the water itself.

• Keep the lid tightly closed and store the tub indoors at room temperature - not in a hot shed or by the pool.
• Check the expiry date. Once opened, a tub is best used within about 6-12 months.
• Never touch the pads, and never put a used strip back in the tub.
• If a result looks surprising, test again with a fresh strip before adding chemicals.
• Very high chlorine (above about 10 ppm, for example just after shocking) can bleach the other pads and give false readings. Wait until chlorine drops before trusting the pH result.

When to get a professional test

Strips are ideal for routine checks. If the water stays cloudy or green despite good readings, if you see staining, or if the readings keep swinging, bring a water sample to a pool professional for a full lab-style test, which can also check metals and total dissolved solids.

Frequently asked questions