Pool Plus sensors feature a special high molarity reference design for stability, reliability and maximum service life in demanding pool and spa applications! Crystallite structure provides a visual indication, alerting you when it is time to order and have an on-hand replacement electrode, before it requires changing. Choose from pH, ORP, or combined pH/ORP Pool Plus Sensors featuring protection against breakage – Available in single junction or contaminant-resistant double-junction models – PP200 series Extended Life: The PP200 series offer double-junction reference for applications where heavy metals, organics, or other chemicals that can poison the electrode are present. Available for pH or ORP.