Natural Resources: The pH of Watering the Garden by Cole-Parmer

One of the handiest tools in a gardener's tool belt is the pocket pH
meter or tester. Within seconds, the meter's display reveals the
acidity or alkalinity of water and soil via the pH reading, indicating
if nutrients are feeding into plants. For gardeners investigating why
their plants are not thriving, the pH reading is, quite literally, a
litmus test.

Priced around $100 or less, the handheld pH meter is also a worthy
investment. Except, that is, when it begins to malfunction. Sluggish
readings that take 15 to 30 seconds to register, erratic measurements
that fail to stabilize, blatantly incorrect values, or no pH display
at all, are complaints common to users of pocket pH meters. Further,
gardeners using rainwater or treated wastewater to irrigate plants may
find that the performance of their pH meter declines rather quickly.
Why?

Regardless of the type of pH meter, the problem can typically be
traced back to the electrode itself. Single-junction electrodes are
much more prone to problems and shorter lives than their
double-junction counterparts