Frequently asked questions

It depends on the application. For daily laboratory use, calibrate before each measurement series, or at least once a week. In an aquarium or pool, every two to four weeks is usually enough. As a rule of thumb: the more accuracy you need, the more often you should calibrate.

Always moist, never dry. The ideal is a storage solution (3 mol/l KCl) in the protective cap. Distilled water is unsuitable, as it leaches ions out of the glass membrane and damages the electrode. A dried-out electrode can sometimes be revived by soaking it in KCl solution for several hours, but there is no guarantee.

Typical signs are sluggish readings that take minutes to settle, failed calibration despite fresh buffer solutions, visible cracks in the glass membrane, or strongly fluctuating values. A slope below roughly 50 mV per pH unit also points to the end of the electrode's life.

With good care, one to three years - even unused, because the electrode ages chemically. Hot, strongly alkaline or protein-rich media shorten the lifespan considerably. Regular cleaning and moist storage extend it.

Gel electrodes are maintenance-free and robust - ideal for beginners, aquariums and pools. Refillable liquid-electrolyte electrodes respond faster and measure more accurately, but need a little care. For demanding laboratory and industrial applications, they are usually the better choice.

Not always. The connector type is decisive - BNC, S7 and DIN are common. Many electrodes with a BNC connector fit most meters and controllers. Before buying, check the connector on your existing device.

It depends on the contamination: limescale dissolves in dilute hydrochloric acid or vinegar-based cleaner, proteins are removed with a pepsin-HCl solution, and grease comes off with mild washing-up liquid. Important: never rub or scrape the glass membrane mechanically - the sensitive hydrated layer will not forgive it. After cleaning, soak and recalibrate.

The zero point is the voltage the electrode delivers at pH 7 - ideally close to 0 mV. The slope describes how much the voltage changes per pH unit; the theoretical value is 59.2 mV (25 °C). The further both values deviate from the ideal, the more the electrode has aged.

If the sample and the calibration buffers differ noticeably in temperature, or the measuring temperature fluctuates strongly: yes. The voltage per pH unit is temperature-dependent. Many electrodes have an integrated temperature sensor for this (recognisable by labels such as ATC or an additional connector).

Better not. Alkaline buffers (pH 9/10) in particular absorb CO2 from the air and shift measurably. Calibrating with a degraded buffer makes all subsequent measurements wrong. Close opened bottles tightly, never pour anything back into the bottle, and watch the expiry date.

Both look similar but measure different things: the pH electrode measures acidity, the redox electrode (ORP) measures the oxidation potential - for example the disinfecting power of chlorine in a pool. The values cannot be converted into each other, and the electrodes are not interchangeable.

Common causes: a dirty or clogged junction, too little movement of the sample, electrical interference (for example from pumps on the same circuit), air bubbles on the membrane, or simply an aged electrode. Cleaning and recalibrating are the first step; if the jitter remains, check the slope.