Hygrometer

A hygrometer measures the relative humidity inside an enclosure, which matters just as much as temperature for species that come from humid forest habitats or that need a humidity spike to shed properly. Too little humidity can cause shedding problems and dehydration, while too much in a poorly ventilated enclosure can encourage mold and bacterial growth in substrate.

Analog dial hygrometers, the round gauges often sold as inexpensive combo units with a thermometer, are widely known among keepers to run inaccurate, sometimes off by a large margin in either direction. Digital hygrometers with a remote probe give a more reliable reading and let the probe be placed at a specific spot in the enclosure, such as inside a hide or near the substrate, rather than only reading the air near the front glass.

Because humidity is not uniform throughout an enclosure, a single reading taken near the front vents will not reflect the humidity inside a moist hide or deep in the substrate where many species actually need it most. Using two probes, one in the general air and one inside a humid hide, gives a clearer picture than a single gauge. Checking and calibrating a hygrometer occasionally, or simply replacing cheap analog dial units with digital probe models, avoids acting on numbers that do not reflect real conditions.