The Neptune Systems Apex Double Junction Lab Grade pH Probe holds calibration longer and has a longer lifespan than single junction probes. Double junction probes have a second vessel inside the main electrolyte with a second internal junction. The means that even when the aquarium water eventually begins to make its way into the first compartment, it still has to go through the second junction to contaminate the electrolyte surrounding the reference electrode.
They're included with the
Neptune Systems Apex System Gold (New Style) w/ Energy Bar 832 .
