A fluid sanitizer includes a substantially cylindrical cartridge for containing sanitizing media such as a silver bactericide. The sanitizer inserts into an existing filter in the normal filter flow path and permits filtering and backwashing. The cartridge is a full flow design and may either be packed bed or loosely packed to become fluidized under filtering conditions. Sand filters with either top-mounted or side-mounted valves may be retrofitted with the sanitizer with no or minimal modifications.
