Product review (5 stars): Increase filter's life
I live in the Mojave desert and need to run the humidifier constantly during the winter.  The swamp cooler adds moisture during the summer months.  I discovered the Holmes humidifier replacement filter's life can be extended IF you allow the filter to dry thoroughly between refills.  Simply continue to run the fan until the needle moves to the red zone.  Turn off the machine, remove the tank, refill the water adding Holmes' bacteriostat, replace.  This system gives me 90 days on one filter.