The Airocide APS-200 PM 2.5 replacement chamber kit has a state of the art cartridge that is unique from the traditional Airocide Cartridge. The two are not interchangeable. If you have purchased the APS-200 PM2.5 unit; this is the cartridge to buy. We still make it easy. Just replace the Reaction Chambers when the indicator light starts blinking, approximately once a year. *For extreme environments, we recommend replacing the APS200 PM2.5 reaction chamber every six months.