Too much chlorine bleach in the humidifier water will make your whole place smell. An eyedropper is a good tool to dispense the bleach every few days. But do be careful with bleach around acids. I keep one of these machines next to my enlarger in the darkroom, so the paper won't curl in the winter. In dry conditions, the emulsion shrinks and pulls the face of the print up.
Humidity swells the emulsion, allowing the paper to lie flat.
Filling these machines becomes a chore in the winter. They can easily evaporate a gallon of water per day. I have found the counter-top types of humidifier to be useless. They tend to be short-lived. It does not evaporate the water and keep the minerals inside the machine.