The tisserand aroma stream cartridge is an individual replacement cartridge designed to be used with the tisserand aroma stream diffuser although your tisserand aroma steam diffuser includes a cartridge it will need replacing after extensive use to ensure maximum fragrance diffusion it is also advisable to use a new cartridge when changing oil blends or when changing essential oil type for example switching from a citrus blend to a floral one to replace cartridges ensure that your aroma