If you know for sure it's very small dust particles - then some mechanical filtration is in order.
If you're not sure what they are - turn everything off in the tank for awhile, except the lighting and watch.
If they rise - they could be very small micro-bubbles of air.
Really small air bubbles sometimes look like particles of dust.
I'm always concerned when I read your posts regarding water quality HNF2K, which stems from the intial set up.
If it's bubbles - mechanical filtration will do squat.
If it's indeed dust - get some fine filter media as nolofinwe suggested. If you can throttle down on the return pump while you run the fine media - this may help keep the trickle plate in the w/d from running over.
Wish you luck