I know, I just like to add info to old threads in the case a new grower stumbles upon this through a Google search. Seems to be one of the top questions new DWC growers ask. I never needed to ask that question because I bought buckets that came with instructions. I know a lot of people buy baskets and buckets and build thier own.
This is exactly how I found it. I just mixed 3 gallons in my rez, roots are about 9 inches below the net pot. Reading this, I may mix one more gallon to get the soup level up to just below the net pot.
Also, in case anyone cares, my solution to the chiller issue is large ice bombs. I have my single DWC bucket (stealth grow) sitting in a 14 gallon tote and I fill it with about 3 gallons of water. I fill gallon milk jugs with water and freeze them. I don't use my freezer much ever, so I rotate out 4 1-gallon jugs and a few Gatorade bottles to keep the temps under control. 2 full gallons of ice will keep my temps in check for about 8 hours, then I'll rotate them out again. The only time I had an issue I was out of town, ice wasn't changed for about 48 hours. But usually I don't have to rotate my ice bombs out but in the morning, when I get home from work and before bed