Cleaning a humidifier tank is extremely important, and will help prolong the life of the unit. Demineralization Tablets will purify the water in your ultrasonic humidifier and reduce or eliminate the white dust build-up, which makes it easier for cleaning. The pack includes 12 tablets, which last up to 3 months. Simply add 1 tablet each week to the water reservoir and watch it go to work. The tablets will continue to work for the entire week, even after the tank is refilled (as long as it is not rinsed out)..