Graco Humidifier Replacement filter for 1.5 Gallon

This is the cheapest replacement filter for our Hamilton Beach humidifier that I found. My only complaint(s) is that it does not say how often to change these filters nor does the packaging offer any advice on how to extend the life of these filters. It seems that they do not last more than a few weeks without drying up or turning brown. I guess that's normal, but neither the humidifier nor these replacement packages tell you how often to replace the filters.Buy Graco Humidifier Replacement filter for 1.5 Gallon!