you can clean the dust out by whipping an egg or two up and adding to the tank.. that will suspend the particles.. i've also seen folks put a sock over their growbed drains for a few days to filter out the "dust"
Whipping an Egg? Like an uncooked omelet? Do you put that in the tank or in the flower bed?
Current Aquaponics System
11 Gold Fish
Aquarium = Custom 90 Gallon Raised Pond on casters
Flower bed = Custom 4' x 8' Flood Table (Bell Siphon)
Bio Filter = 6 Gallon Polypropylene Tote with Hydroton (Bell Siphon)