Sorry here also Cecil... Now back to your system, some questions:
How deep are your tanks?
Length and width? I'm guessing 2' by 16' (per side).
No reason to be sorry!
Sides and divider are 2 X 12's with the tank 8 feet long and 4 feet across.
Water depth is probably 9 inches or less due to the foam board and plastic culvert pipe that holds on the double layer of greenhouse plastic.
Do you have some kind of bracing system around the tanks? (to keep water pressure from bowing it out)
No need. Sides are all 8 feet long 2 X 12's with a 1/2 inch plywood bottom. There is also 2 X 6 ribbing under the plywood to support it. The water really isn't deep enough to produce much out pushing pressure.
About a pound and half or so. 11 to 14 inches. WAG.
Is the black tile just to hold the liner down?
Yes. It's black tile with a slit cut lengthwise that wedges the plastic down.
One more thing, is that enough water movement to keep the fish tank fairly clean and nitrite levels down?
Yes! The fish provide movement, and the center plume from the diffuser pushes water up and down toward the center drain. I once used a horizontal and vertical spray bar but have found in tanks this small it's not necessary. (4 to 5 feet in diameter).
A gate valve in line with the external stand pipe is pulled a 2 times a day to flush solids near the drain and in the drain.
This waste water is used to water the conventional raised garden that is adjacent to the fish tank. Since the tank is so much higher than the raised garden, I can water the garden with it via gravity by opening the gate valve and directing a hose anywhere I want.
Same goes for water changes as there is not only an external stand pipe and drain line that comes from the center drain, but also a drain line from the clarifier tank.
