I bet your dust is coming from the cool mist humidifier. Clean that thing out really well, and be sure you are using distilled water, or at least low ppm RO water in the humidifier. I don't think the dust is coming from your CO2 source. If I'm right, the dust isn't really harmful, just the crud out of your water/humidifier.
You have it set too high and moisture is re-solidifying on the cold tank/regulator. Its pretty normal just turn it down a little and for the most part it was stop happening.