Agree. However, make sure that what you see is mold and not florist foam pushed out of the humidifier. Had one instance when I thought I was looking at mold, but actually the foam in the humidifier was powdered (vibration from traveling, long shelf life, who knows) and when solution was added it caused it to appear on the outside of the slots, where it dried. Looked for all the world like mold, but actually wasn't.