I think the schedule and manner of replacement depends on the use of the chain. For example, although I keep about 250' of chain, I most often
anchor in ca 10' depths that are common in
Florida and the
Bahamas. This means that I have far more
corrosion nearer my anchor, so I usually buy a shot of about 50' and add it to the bitter end after cutting off a length nearer my anchor. I connect lengths of chain with Crosby schackles and lock wire their pins. They don't ride as smoothly over my chain
gypsy, but all the proper sized connector links I've tried corrode at twice the rate of my chain,- of course they can be inexpensive to replace. I have an open
gypsy on a manual horizontal
windlass, so I can do this. Many
electric windlasses will jam with these schackles. If you replace segments of chain in a schedule like this, you will be able to
purchase lengths that can be shipped at a 100lb rate. This gives you a much wider
shopping and
delivery range. I don't regalvanize,
paint, or chemically treat (ospho) my chain, but some do.