Keep pool and drinking water in balance.
pH, conductivity and clarity readings for pools, hot tubs and drinking water. Tap a problem to jump to it.
Green or cloudy pool water
Why it happens
Chlorine works much less well at high pH. PWTAG lists low free chlorine, failed circulation and high pH among the main causes of cloudy water.
How to tell it apart
If you can't clearly see the bottom at the deepest point, the water is too cloudy to use. Cloudiness can also come from air in the system, scale, algae or poor filtration, so check pH and chlorine first, then the plant.
How to test
- Calibrate the pH probe before use.
- Sample away from dosing points and returns.
- Record pH alongside your chlorine test.
A monitor such as the PH-W3988 measures pH, EC, TDS and temperature.
Good and bad readings
| Measurement | Recommended |
|---|---|
| pH (chlorine disinfection) | 7.0–7.4 |
| Turbidity | 0.5 NTU is a useful guideline; above this water is unacceptable |
Source: PWTAG Technical Note 34, Cloudy water.
What next
Correct pH, then chlorine. PWTAG says a pool failing these checks should be closed for investigation.
Common mistakes
Not calibrating the probe; sampling next to a dosing point.
Instrument for this step
PH-W3988 6-in-1 WiFi Water Quality Monitor - pH & TDS Water Quality Tester WiFi£78.99
Hard water, scale and drinking water (TDS/EC)
Why it happens
Dissolved minerals raise TDS and conductivity (EC). Hard water leaves scale in kettles, showers and heaters, and water from private wells can change with weather and ground conditions.
How to tell it apart
Compare with your usual readings; a sudden change matters more than a single figure.
How to test
- Run the tap before sampling.
- Measure pH and conductivity with calibrated probes.
- Record results with the date.
Good and bad readings
| Indicator parameter | Specification |
|---|---|
| pH | 6.5 minimum, 9.5 maximum (at consumers' taps) |
| Conductivity | 2500 μS/cm at 20°C maximum |
Source: The Water Supply (Water Quality) Regulations 2016, indicator parameters.
What next
We have not found a sourced UK figure for TDS and scale to quote here; for softening advice ask your water supplier. These meters check indicators only, not bacteria or chemicals. If readings are outside the range, contact your water supplier or, for a private supply, your local council.
Common mistakes
Treating a pH/EC reading as a safety test; uncalibrated probes.
Hydroponics and tanks: continuous monitoring
Why it happens
In pools, hydroponic systems and tanks, nutrients, dosing and evaporation change the water between spot checks.
How to tell it apart
Logged trends show whether a reading is a one-off or a drift.
How to test
- Place the probe where water circulates.
- Calibrate as the maker recommends.
- Review the logged trend, not just the latest value.
What next
Set your own alert levels from the ranges above.
Common mistakes
Leaving probes uncalibrated for months.
FAQs
Does a pH meter replace chlorine tests?
No. Test chlorine separately.
Can I use it on drinking water?
It measures pH, EC and TDS. It doesn't test for bacteria.
Can I get a VAT invoice?
Yes. All prices include VAT and VAT invoices are available.
Need help choosing?
Contact us and tell us what you need to measure.
Photo credits: Green or cloudy pool water (pH and chlorine): photo by Asurnipal, CC BY-SA 4.0, Wikimedia Commons, Fraxern-dye experiment perfusion-swimming pool (10-51)-46ASD.jpg (https://commons.wikimedia.org/wiki/File:Fraxern-dye_experiment_perfusion-swimming_pool_(10-51)-46ASD.jpg); Hard water and scale (TDS/EC): photo by Tim36272, CC BY-SA 3.0, Wikimedia Commons, A frost-free silcock faucet with calcium buildup .jpg (https://commons.wikimedia.org/wiki/File:A_frost-free_silcock_faucet_with_calcium_buildup_.jpg)