I had trouble finding instructions for the small system I wanted to make, and had to pull information from various sources. Here are the results of my research and experimentation over two months.
Step 1: Shelving/Support
Step 2: Principles
1) depth of water for the roots of intended plants
2) distance between plants and lights
3) roots don't like light, so choose opaque tubs
4) limit debris in water from medium
5) strength of light needed for type of plants grown. 45 watts per fixture should work for the lettuce I'm growing.
6) the water needs to be well oxygenated
7) the top of the syphon needs to flare out to facilitate an even flow
8) the last elbow at the bottom of the drain is used to regulate flow
Step 3: Materials
1 fish tank, about 20 gallons
1 water pump, about 150-300 gph
1 water heater, optional
Two light fixtures (third optional)
3 inch mesh pots
rock wool plugs
5 ft of tubing
Clips and clamps
1 mylar emergency blanket
2 concrete mixing tubs or similar
2, 3/4 inch bulkheads (found online)
2, 3/4-1.5 inch double slip reducers
Length of 3 inch PVC pipe
2, 3 inch PVC pipe caps
Length of 3/4 inch PVC electrical conduit
4, 3/4 inch PVC elbows
Step 4: Bell Syphon
First, install the bulkhead in a corner of the tub, avoiding raised areas that won't seal well. The rubber gasket goes to the bottom. Cut several lengths of 3/4 inch conduit:
2, 2 inch segments
2, 6 inch segments
2, 15 inch segments
Put the 15 inch segment below the bulkhead, and the 2 inch segment on top. Put the reducer coupling on the 2 inch piece. The height of the water is dependent on the length of the 2 inch piece, so it is variable. Also, the 15 inch piece is variable depending on the height of your plants.
Put the elbow beneath the 15 inch piece and the 6 inch piece on that. Then put on the last elbow.
Finally, you need to cut the 3 inch PVC to one inch above the height of the syphon. Make some sort of holes on the bottom of the tube, and cap the top, drilling one hole for air. I used my dado kit to cut crenellations like a castle tower.
Step 5: Finishing
Give the fish somewhere to hide, and add a heater if the temperature goes below 70 F.