> Maybe my tap water has more minerals than your tap water

Unlikely; my tap water is well water. I do clean the humidifier with vinegar every week to keep the mineral buildup down. Then again, I do that with the shower head and tea kettle too (though a bit less frequently).

The big thing, as I've found it, is keeping the output down to a visible minimum. A big plume of mist that visibly lands anywhere isn't adding more water to the air - it's putting water droplets on the surface much like a spray bottle. It looks good, but isn't doing the job you're asking it to.