Clay candles need not be replaced, if these are cleaned and rinse washed regularly. But in case of arsenic or fluoride adsorbents, a change is required at least once in 2 years. The local PPB or PPM levels of arsenic and fluoride has to be considered to see how long the adsorbents can work. It may vary across water in different places thereby enhancing or reducing the life span of the add-ons.