The effective usage time of the filter depends on a number of factors: – Concentration of contamination – Breathing rate – Heat – Humidity – Hygiene factors,
and your environment. As a role of thumb, you should change the filters when the white filter turns 50% grey as printed on the filter packaging.
On the other hand it is recommended the filter should not be used longer than 2 weeks, even if there is no signs of color change.
The filter will slowly lose it's effectiveness once started using.