To determine if your Z-Ion electrode rods need to be replaced, please first reference: https://support.katadyngroup.com/518809-Z-Ion-Service-Light-Lit
Early generation Z-Ion bowls did not have removable rod assemblies. First, identify if your bowl/rod assembly is the old style one piece, or if you have the newer style threaded rods. Old style is one piece and all grey, whereas the new style uses a grey base and black threaded assembly for the electrode rods. Examples seen below for reference.
If you have the older style, replace with SUB-ZION-ELECTB as seen in the above image.
If you have the newer style removable rods, replace with SUB-ZION-RA.
When replacing the newer style rods in the field, it is important to hold the grey base in place so it does not break the seal with the bottom of the filter housing when the rods are threaded in or out. See below image for an example, in the factory a wooden jig is used to hold the base in place, but the same can be achieved with a wrench or similar tool.