Test strips are the most widely used pool testing method. Used correctly, they provide fast, reasonably accurate readings for most parameters. Used incorrectly, they give readings that lead to unnecessary chemical additions.
Key Facts
- Dip the strip into pool water for exactly 1–2 seconds — longer soaking washes off the reagents.
- Read results within 30–60 seconds of removing the strip — colours continue to change after that.
- Store strips away from heat, humidity, and direct sunlight to prevent reagent degradation.
- Premium 7-in-1 strips test: FC, TC, pH, TA, hardness, CYA, and bromine.
How Test Strips Work
Test strips have separate reagent pads for each parameter being tested. Each pad contains a dry chemical reagent that reacts with the parameter it is designed to detect, producing a colour change. The intensity or shade of the colour is compared to a reference chart on the bottle to determine the measured value. The chemistry is similar to liquid test kits but pre-dosed and dried onto the pad, which makes them faster but slightly less precise — especially for measurements near the boundaries of acceptable ranges.
Correct Technique
Collect the sample from mid-pool, about 18 inches below the surface, away from any return jets. Do not dip directly from the surface. Hold the strip by the end that has no pads and dip it into the water for the time specified on the bottle (typically 1–2 seconds). Remove it and hold it horizontally (do not shake it). Compare each pad to the colour chart within 30–60 seconds in natural light. Squinting at the strip under indoor lighting is a common source of misinterpretation — compare in outdoor light or under bright white light if possible.
Storage and Accuracy
Test strips degrade over time when exposed to humidity, heat, and UV. Store them in the original sealed container with the desiccant, away from pool chemicals, sunscreens, and steam. Never store strips in the pool house or bathroom where humidity is high. Check the expiry date on the bottle — expired strips give unreliable results. For parameters where precision matters most (free chlorine, CYA), verify strip readings with a liquid DPD test kit at least once per month.
Examples
A pool owner dips a strip for 10 seconds, then shakes off the water and reads it 2 minutes later under artificial light. The chlorine pad reads zero. They add a full shock dose. Re-testing with a liquid kit the next morning shows FC at 8 ppm — dangerous for swimming. The strip reading was wrong because of over-soaking, delayed reading, and poor lighting. The correct procedure: 1-second dip, read within 45 seconds in natural light.
Common Mistakes to Avoid
- Soaking the strip for more than 2 seconds, which washes reagents off the pads and gives artificially low readings.
- Reading results after more than 60 seconds, when colour changes no longer correspond to the reference chart.
- Storing strips in a humid area (poolside, bathroom) where the desiccant cannot protect them.
- Pool & Hot Tub Alliance — Pool & Spa Operator Handbook, 2022
- Taylor Technologies — Pool/Spa Water Chemistry Reference