Start monitoring ORP, replace your ORP probe or add one for another tank

Buy this probe if you are:
You measure ORP in your aquarium with an Apex System or a PM1 module
replacing a worn out ORP probe (we recommend you replace your Lab Grade ORP probe every 18-24 months).
adding another tank to your system, want to measure ORP in it, and purchased a PM1 to do so.
want to have a back-up probe on hand

Lab Grade Probes tend to last longer, give more accurate results, stay calibrated longer, and need replaced less frequently