First, thanks to you, the Rubbermaid tote DWC lettuce is growing like crazy and haven't all died of root rot from a too-high water level!
Second, GPS, I've been thinking a lot about your design, mainly because I'm in the midst of building my own 12' x 20' greenhouse in order to grow hydroponic lettuce, tomatoes, peppers for my family. This thread and both of you, have been a huge inspiration. [Raises a frosty mug of root beer in toast to you]. Thanks!
Anyway, GPS, here are some thoughts I've had about your design...
1. Smart. Your black plastic rolled over elastomeric on a frame idea is REALLY clever. How you came up with this idea, I don't know, but it's very smart. I think I will try this for levels 2 and 3 of my greenhouse.
2. SWC - "Shallow" Water Culture
You said that you were thinking of 4" to 6" inch depth of water for your shallow-rooted herbs. I would normally be concerned that a thin water mass may not stay cool enough in summer (or may get too cold in Winter) for the plant roots, but you said that you plan to recirculate the water which overcomes that concern; however, I wonder whether having multiple smaller recirculating systems rather than one large one might make sense (e.g., so that 1/2 strength nutrients
of one pH / TDS level could be recirculated to seedlings, heavier concentrations and/or other pH level solutions could go to more mature or different varieties of plants, etc.)?
3. Fish. I'm wondering whether it makes sense to experiment with a couple hundred gallon talapia-stocked "aquarium" (a tank lined with pondgard EPDM)? Feed the fish their fish food and let fish output feed the plants? The bonus is fish to eat and/or sell for $3.00 per pound wholesale. Do you have any thoughts about this? Do you think this might have a chance of working?
4. Greenhouse. I'm planning to cover the inside frame walls of my greenhouse with fiberglass window screen then, on the outside, constructing a hinged frame hung from the top of the frame wall to which I'll attach Lexan corrugated fiberglass panels. These panels will be able to be swung open on hot Summer days for breezes while keeping out most larger bugs; during Winter months, just close it up and it will act like a normal greenhouse. Though the screen may block 15-20% of light from the walls, I'm in Florida so light should still be adequate. Do you have any thoughts or suggestions for improvement to this plan? This same concept could be adopted for a 6 mil plastic cover, incidentally.
Again, thank you both for your excellent comments!