The first expansion module, the PM1 (shown above) , with a pH or ORP, temperature, and 6 digital inputs. The PM1 features are:

• Monitor/Control pH or ORP, and temperature.
• 6 digital inputs for float switches, water on floor sensors, pressure sensors, etc.
• Full datalogging support in Apex Base module.
• Up to 240 AquaBus modules can be added to the Apex system.
• Plug and Play.  Automatically recognized when installed into the system.
• Two AquaBus connectors for flexible expansion via AquaBus
• Led Status Indicator
• Upgradeable firmware.
• Compatible with Apex and Apex Lite systems.
• Galvanic Isolation for accurate and reliable probe readings.
• Comes with 3' AquaBus cable.
• Probe not included.