# pH meter

> A pH meter measures solution pH with a glass electrode whose voltage changes with hydrogen ion activity; it needs regular calibration and a moist probe.

- Canonical: https://genetixbay.com/knowledge/glossary/ph-meter.html
- Also written: pH pen, pH probe, pH tester, pH electrode, digital pH meter, pH meter probe
- Glossary category: pH, EC and water · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

A pH meter measures the voltage between a glass sensing electrode and a reference electrode, usually combined in one probe, and converts it to [pH](https://genetixbay.com/knowledge/glossary/ph.md). The thin glass bulb develops a voltage proportional to the hydrogen ion activity in the sample. Pens put the probe and meter in one body; benchtop and portable meters use replaceable probes on a cable.

## In practice

Care rules that matter:

- Keep the bulb wet. Store it in storage solution (usually 3 M KCl), never in distilled or [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md), which draws ions out of the reference.
- Calibrate with fresh buffers, at least weekly for hydro and before important readings.
- Rinse after use; nutrient and organic residues coat the glass and slow response.
- Probes age. Typical life is around one to two years with good care. Slow, drifting readings and low slope mean replacement.

Liquid drop tests and paper strips work for rough checks but are hard to read precisely in coloured nutrient solutions.

## Don't confuse with

- **EC meter**: measures salt strength, not acidity; many combo meters do both, with separate probes or sensors.
- **Soil pH probe (two-metal type)**: inexpensive analogue probes are unreliable for growing decisions.

## Related terms

[Two-point calibration](https://genetixbay.com/knowledge/glossary/two-point-calibration.md), [Calibration solution](https://genetixbay.com/knowledge/glossary/calibration-solution.md), [ATC](https://genetixbay.com/knowledge/glossary/atc.md), [pH](https://genetixbay.com/knowledge/glossary/ph.md), [EC meter](https://genetixbay.com/knowledge/glossary/ec-meter.md)

## Read more

- [pH and EC meter calibration: buffers, slope, storage and when to replace a probe](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md)