Can't be used much if it lasts two years I would say. I maybe get 3 or 4 months but that is washing 3 cars at least weekly. Then I bought another canister and use the older resin as a pre filter which makes the good stuff work less hard and now lasts longer.
Used quite regularly. But the water up on my area isn't that hard to begin with. That's why I can get up to two years with it.