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We used Ultrasonic humidifiers in a server room (to cut down on static risk) and I can confirm they get covered in minerals

Amazon reviews on ultrasonic humidifiers complained that their expensive home electronics died because of the dust.

Hah, well I don't work there anymore. They did have reverse osmosis water filters on them, but no air filters.

Turn them down (ideally to the point where you can barely see the mist). They don't have to run at full blast to be effective.