When do the resins in the softener tank need to be changed?

With the proper pretreatment and maintenance, the average water softener will not need its resins replaced in its lifetime (20 + years). It is impossible to accurately determine the life of resin since so many factors contribute to the degradation of the resin itself.

Note: Proper pretreatment can be a simple as a sediment filter or as complex as chemical injection system combined with a multimedia bed, this is determined by having your water tested.