@RandallFlagg,
the round cylinder is the conditioner,the square only holds the salt to make brine to clean/regenerate the resin inside the round tank. The resin is actually the filter media and should last a long time. For the original owner Rainsoft offers a limited lifetime warranty, so hopefully yours will last a long time. If you're on city water , the resin probably has some carbon in it to remove the chlorine,not alway though. You'll be able to tell if once you regen ,the water still smells like chlorine. There is not really a filter that needs replaced, but from time to time it may need serviced, just like a car. Try what I said earlier and let me know what happens. Then we can talk about how much salt to add.