Do the new Differential Cation sensors need to be recalibrated regularly?

Yes. The Cation Differential pH and ORP sensors have a glass electrode that needs a 2 point calibration performed regularly. Because of the Cation Reverence electrode you must use special buffers with a constant sodium ion concentration. This calibration is needed to compensate for the change in response of the glass electrodes. These changes are normal and are caused by aging or chemical attack, and they are accelerated at higher temperatures.