TruSens Replacement Filter for the Medium and Large TruSens Ultrasonic Humidifiers | Keep your TruSens Humidifier running at optimal levels. The enhanced water softening filter minimizes mineral build up and white dust for a cleaner mist | Maintain your TruSens Humidifier by changing the filter at regular intervals | The enhanced filter softens hard water to minimize mineral build up to deliver a cleaner mist. This also helps to prolong the life of the humidifier | One filter lasts approximately 4 months for a full season of humidified air | The filter can be used with TruSens medium or large humidifiers, models N-200 and N-300 | Change indicator light is displayed on your humidifier when the filter needs to be replaced