My RDWC uses 5 gallon buckets. The plants grow in 8"netpot bucket lids that fit snugly over the top of the 5 gallon buckets, sealing out light from above. To complete the dark environment inside, I painted the RDWC buckets and I'm sure to fill the netpots with soil about 3/4 full to cover the holes.
The key difference you're looking for is the hybrid nature of my system; I use 50/50 coco/hydroton as the media, and I topfeed through it. The water is pumped from the RDWC beneath, and the buckets get watered to at least 30-60% 'runoff', although it just drains down through the media, roots and back in to the RDWC bucket below. Because this gives so much room for beneficial microbes, I'm guessing this is why I haven't had any more problems with pythium or the like.
The airstones were huge for encouraging the roots to come out of their coco nursery and play in the airspace beneath the netpots and ultimately drop into the water below. When things are just right, I've measured 1.5" of growth a day in veg. for several days running. In bloom, stretch really takes on a Fantastic Four quality, and then the buds get so fat so fast they're breaking branches in week five?!
I use a chiller, all right- just one. It sits in the office all winter, generating enough heat to warm the whole house. It cools everything; RDWCs, and the sealed rooms. At the risk of digressing a little bit, I am also using the water cooling system to dehumidify the sealed rooms, and I just may have hit upon a way to do it at above 100% efficiency. Long and short, just the one 2 ton chiller cools all aspects of 16 lights' worth of growing space. In the summer- in a record breaking heatwave... with enough capacity left over to provide airconditioning for the house. SERIOUSLY.