i appreciate your reply Oliver..
i'm a member of several forums (aquaponics, ponds etc) and try to learn as i go.. i was at a presentation for a guy selling systems, everything was galvanized, fish tanks, gb's.. and when i questioned him about it he stated that he'd been doing it that way for years with no issues.. on another forum i follow someone experienced some fish deaths, and had galv tanks (not lined), after this happened to a couple people someone got the smart idea to have their water tested and found toxic levels of metals that had leached from the tanks..

on the byap forum they are trialing 3 growbeds side by side from one ft, one is cf, one is flood and drain and one is timed flood and drain, the cf bed has been showing better performance of all but a couple of plants, it's easier to follow a recommendation when there is visual proof..

your point about DO levels has been demonstrated on many forums.. gb depth though, i've seen great performance out of "shallow" beds and planting things that don't need the depth, but personally i think deeper would be better, there's a system of one of the members here (TCLynx) that is using rubbermaid totes for gb's 20" deep, these aren't being "completely" drained because she drains out the side, again she shows tremendous results..

i take pretty much everything i read with a grain of salt, but with a well documented system (pictures/dates etc), including failures/issues etc beats the hell out of a verbal argument every time

i'd be interested to know how you arrive at that stocking density as well...