Product review (5 stars): This will keep your humidifier clean and sanitary.
Do you know what "Legionnaires Disease" is?  If you did everything wrong in the use of a humidifier, this could be the result.  Ever leave a wet sponge in a sink for too long?  It gets nasty.  It can hold lots of bacteria and odor. Use this anti-bacterial additive to the water tank reservoir once a week. It  will destroy algae, mold, bateria, etc. that can grow in a humidifier filter/wick.

This is an aftermarket bacteriostatic treatment, since Kenmore is the manufacturer of the humidifier and sells its own additive.  I can find no discernable difference between the name brand and this aftermarket alternative, other than price and availability.

FYI:
Also throw out (or replace if you live in Alaska) the filter at the end of the winter season.  Clean your humidifier (with the filter removed) before storing it for the summer.  Otherwise you will have a much bigger and nastier job come next winter!