Product review (5 stars): Works great
Keeping the mildew and scum out of my humidifier used to be one of those eternal winter struggles.  Even when I added a few drops of bleach to the water, the scum would form in 24 hours.  I'd have to completely clean and bleach it every few days.

I stumbled across this product and gave it a go.  I've been using it for about a month, and the humidifier has no trace of scum or mildew.  It works great, and I am very happy.  A 32 oz bottle will treat 196 gallons, so its very affordable, too.

I use it in a cool mist humidifier and it works fine.

My only tip is to fill your resevoir first, and then add this product.  Otherwise it foams up badly.