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. 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, 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.
pH measures how acidic or alkaline a solution is on a 0–14 scale; in growing it controls nutrient uptake, with soil best near 6.0–7.0 and hydro 5.5–6.5.RO water is water stripped of most dissolved salts by reverse osmosis; it has near-zero EC and little buffering, so pH moves easily and Ca and Mg must be added.An EC meter measures how well a solution conducts electricity, giving nutrient strength in mS/cm or as ppm via a conversion factor.Two-point calibration sets a pH meter with two buffers, usually pH 7.00 then 4.01, fixing both its offset and its slope for accurate readings.A calibration solution is a standard liquid of known pH or EC used to calibrate meters, such as pH 4.01, 7.00 and 10.01 buffers or 1.413 mS/cm EC standard.ATC (automatic temperature compensation) is a meter feature that corrects pH or EC readings for sample temperature, usually referencing EC to 25 °C.
