|Pari Nebulizers come standard with a very small, white air filter. Over time, if these filters are not replaced you can begin to see diminished effectiveness of your Pari nebulizer. Easy to replace, you simply remove the small plastic cap with a coin and replace the white filter. For some units, you can use the included tool to remove the old filter. The replacement filter fits all long lasting Pari nebulizers, including the Pari Ultra II, Trek S, and Pari Vios nebulizers. Generally, check to see if the filter is dirty every six months when you replace your neb kit, and replace after approximately 500 hours of use.