I’ve always had issues with white dust with ultrasonic humidifiers, but perhaps something like this may help.
isinlive Demineralization Cartridge Compatible with HoMedics Ultrasonic Humidifiers, Filters Mineral Deposits, Prevents Hard Water Build-Up, Purifies Water, Eliminates White Dust and Odor, 16 Pack
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We currently have 2 of these:
Amazon.com: AIRCARE Nutmeg Digital Style Whole House Pedestal Evaporative Humidifier for 2400 sq. ft: Home & Kitchen
And one of this:
Venta LW25 Airwasher 2-in-1 Humidifier and Air Purifier in Black
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The Venta one is more expensive, but doesn’t require filter changes (like the aircare one which are about $20/each).
These are the filters it takes:
AIRCARE 1043 Replacement Space Saver Wick (2)
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The Aircare one holds more water, so requires less frequent fills.
I think, i would prefer having a larger Venta one, they also have a larger one (2.6 gallons vs 1.8 for the other one):
VENTA LW45 Comfort Plus Airwasher Humidifier, 645 ft², Black
Amazon.com: VENTA LW45 Comfort Plus Airwasher Humidifier, 645 ft², Black: Home & Kitchen
Also the nice thing about the Venta one is that you can take it almost completely apart and almost the entire thing is dishwasher safe (although they say to use a rinse cycle, and my dishwasher seems to lack that feature, but putting it into quick wash seemed to work just fine, even though it washed with hot water).