Carbon filter is a replaceable element of the Allergy and Flu HEPA drum filter, indicator light glows red on your air purifier when the filter needs to be replaced, compatible with the Allergy and Flu HEPA filter drum for all Leitz TruSens Z-1000 air purifiers. This filter with activated carbon pellets offers a level of defence against unwanted odours & VOC's that can invade your home. This carbon filter is a replaceable element of the allergy and flu HEPA drum filter with activated carbon pellets offering a level of defence against unwanted odours and VOCs that can invade your home Specifically designed to remove odours and VOCs from the air, this carbon layer is compatible with the allergy and flu HEPA filter drum for all Leitz TruSens Z-1000 air purifiers. To keep your air purifier performing at its best, it's recommended to replace the allergy and flu carbon filter every 3 - 4 months (depending on usage) . Best for allergies and flu Pack includes: 1 x Carbon filter Compatible