Product review (5 stars): Prevents slimy water tank and humidifier unit!
This product is very helpful for me, as I have a well so my water is not treated at all with chlorine etc and my humidifier gets slimy a day after filling it.  With this product, my humidifier does not get slimy, though cleaning every week is still advised.  Note that this product cannot be used in ultrasonic humidifiers, only evaporation/the ones with the fan.