Neptune Systems Temperature Probe For Apex ControllersTEMPERATURE PROBE EXTENDED LIFE REPLACE YOUR TEMPERATURE PROBE, ADD ONE FOR ANOTHER TANK, OR PUT ONE ON YOUR PM2 PM3 MODULE FOR TEMPERATURE COMPENSATED READINGS Buy this probe if you are: Replacing an old probe Adding another tank to your system via a PMx or ASM module Want to have more accurate readings on your PM2 PM3 modules by adding temperature compensation