What is the life expectancy of a water softner resin?

I have an industrial style installation which we have had for 10 years
with no problems. I assume it is a zeolite based resin but really don't
know (no documentation left by installer).

The resin is in a tank (like gas cylinder) about 4-5 feet tall 8 inches
or so in diameter. No obvious way to ever change the resin. The salt
and saline solution are in another garbage can plastic bin. The
electronic mechanism for recharging etc is mounted on top of the resin
tank via a stem that screw mounts over the top of resin tank?

Softner still works just fine. Just wondering how long they would last?
Indefinitely? Assuming no contamination from city water supply.


Thanks.

Morenuf
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lid