Product review (1 stars): Mislabeled product title - not for just any 'cool mist' humidifier
The product description on the synposis listings for this product reads: "Controls Bacteria and Algae Growth For Cool Mist Humidifiers".

Most 'cool mist' humidifiers use an impeller or ultrasonic mechanism to vaporize water.  Holmes, however, manufactures a wick-based humidifier that they market as a 'cool mist' unit (Holmes HM1300BF-UM Cool Mist Humidifier) -- and THAT is what this product is intended for.  Put this into what everyone else calls a 'cool mist' unit, and as another buyer also observed, your lungs will start hurting after a few minutes.  Thank goodness I was a little paranoid.

This appears to be the only product for use with a regular 'cool mist' humidifier -- but I don't think it will stop slime build-up: http://www.amazon.com/BestAir-UltraTreat-Ultrasonic-Vaporizer-Treatment/dp/B00K8FL9A2