When it’s time to change your filter, make sure that you always have a replacement ready. The Safety 1st True HEPA Replacement Air Purifier Filter removes 99.97% of airborne particles*, so there is less dust, pollen and pet dander in the air. With less contaminants in the air your child’s nursery, or any room where you place the air purifier, will have cleaner and fresher air to breathe. How do you know when to change your filter? When the cumulative use time of the filter reaches 1000 hours, the startup night light flashes for 1 minute, and the single flashing dark gradient cycle is 2 seconds. The filter replacement timing is based on usage. For instance, 1000 hours would equate to about 90 days with daily usage of 11 hours, while 24 hours of continuous usage would require a filter change sooner. *Filter removes 99.97% of airborne particles sized 0.3 microns and above.