How to Read Pool Test Strips
Test strips are quick and cheap, but small technique errors lead to consistently wrong readings — and wrong readings lead to wrong doses. Here is how to get the most reliable result.
Step-by-step technique
- 1Hold the strip by the plain end — do not touch the coloured pads.
- 2Dip the strip into the pool water for 1–2 seconds, away from the return jets.
- 3Remove the strip horizontally and do not shake off the water.
- 4Hold it still for 15–30 seconds (check your brand's instructions — timing varies).
- 5Compare each pad to the colour chart in natural daylight, but not in direct sun. Colours look different in shade versus bright light.
- 6Read from the pad end upwards, noting each value before moving to the next.
What the pads measure
All readings are in ppm (parts per million) except pH, which is a scale from 0–14.
Not all strips test all five — check your brand. Basic strips often skip stabiliser and calcium hardness.
Common mistakes
Reading in direct sunlight
Colours shift in bright light — move to shade or read indoors.
Shaking the strip dry
This removes the sample and distorts the reading. Keep it horizontal and let it drip.
Waiting too long
Most pads over-develop after 60 seconds. Read within 30 seconds of dipping.
Testing near an inlet or jet
Chemical concentration varies around jets. Test from the middle of the pool, away from returns.
Using old or poorly stored strips
Strips degrade once the tube is opened. Seal the container tightly and check the expiry date.
Testing right after shocking
At very high chlorine levels (above 10–15 ppm), the chlorine pad can bleach white and read as zero — a false low. Do not add more chlorine based on that reading. Wait until FC returns to normal range before testing, or use a DPD liquid test kit which handles high levels accurately.
Trusting pH when chlorine is high
High chlorine (above ~5 ppm) interferes with the pH colour indicator and can give a false reading. For accurate pH, test when FC is in the normal 1–3 ppm range.
Stabiliser (CYA): the hardest pad to read
The stabiliser pad on test strips is notoriously unreliable.
The colour change is very subtle and hard to judge accurately. For a more reliable stabiliser reading, use a dedicated liquid test kit — it works by adding drops to a water sample until you can no longer see a dot through the tube, which is much easier to judge than colour-matching.
Stabiliser matters for calculating the correct shock dose — an incorrect reading leads to a significantly wrong amount. When in doubt, use a liquid kit or leave stabiliser blank and enter it manually after a proper test.
Using AI to read your strip
PoolScan uses AI to read the colour values from a photo of your strip. This removes the subjectivity of comparing tiny colour swatches in variable light — the AI sees the actual colours in the image.
Tips for a better scan:
- •Natural light, not direct sun.
- •Hold the strip close — the pads should fill most of the frame.
- •Take 2–3 photos from slightly different angles — the AI uses all of them together.
- •Photograph the colour chart on the back of the bottle alongside the strip for the most accurate result.
Like manual reading, AI results are approximate. Always review the values before adding chemicals, especially the stabiliser reading.
Scan your strip with AI →Photograph your test strip and PoolScan reads the values automatically — then calculates your treatment plan.
Scan your strip →Shop on Amazon
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