Filter replacement is essential for your air purifier to perform at its best | The activated carbon layer removes certain gasses and odours from the air | The carbon pre-filter not only captures odours and gasses, but it also offers the first level of defence against dust and pet hair | This layer is what needs to be replaced on the HEPA drum filter | For best results, replace carbon layer filter every 3 months | Change indicator light is displayed on purifier when filter needs to be replaced | Compatible with TruSens Z1000 Air Purifier