Tech note
Water-Detect Feature in the HOBO MX2501 pH Logger is Not Working

The HOBO MX2501 pH logger's battery-saving water-detect feature is only guaranteed to work in water with at least 100 µS/cm conductivity. The water-detect nodes rely on the water closing the circuit between them. If the water is too fresh, the nodes will not “see” that the logger is in water.