Product review (5 stars): Works great and a bottle will last all winter
This stuff (a capful at a time) will keep your humidifier's paper water filter from getting mold all over it.  Works great and a bottle will last all winter.  In fact after I stopped using the humidifier, I left it setting with the filter in it for about 3 weeks, took the filter out expecting it to be black with mold but there was NONE.  Ordered another bottle for next winter.  Cheaper that buying $20 filters every month.