Peter Hemmings wrote:
Can someone tell me if there is such a substance,

From my (limited) experience, I understood that there is some substance
which can 're-activate' the resin, but it would only be required if the
resin had been exposed to iron fouling from rusty pipes or tanks. The
iron had a greater affinity for the resin than sodium or chlorine. The
resin should otherwise last indefinitely.

You can remove some bacterial fouling by putting a small amount of
chlorine bleach in the salt tank and regenerating.