Every couple of years? Damn it. Ive changed mine yearly and it was gone. Granted I have a Beta 50, and the zinc is on the smallish side compared to others which I have seen. And I have not been very religious about flishing with freshwater everytime I leave the boat
behind for extended periods. This will be part of my new list of decomissioning events
My new zinc exchange policy is probably going to be to check and probably change every six months.