Do you know what type it is... I had a SpectrPure that changed color whrn it was spent... I know that one can be recharged by flushing it with some sort of chemical solution, depends on the cartridge, anion or ionic...
could try calling Craig Winter too at Advanced Quality Water Solutions ( aka EnvirInvestigations)) too.. not sure of his number, should be in the phone book, a pretty straight up gy, I dealt with him when I worked at the lab and he has fixed many of our water issued here at home..
denise