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 – PP100 series Basic: The PP100 series offers single-junction reference for clean water applications. Available for pH or ORP.