There are many different types of hydroponic units available. The best type is the one that suits the plants you want to grow, your building skills, and your available time and space. The ebb and flow (also known as flood and drain) system uses a pond pump to pump nutrient solution into the grow tray where the plants' roots are exposed for 10 to 15 minutes, then it drains back into the reservoir for 45 to 50 minutes. This cycle runs continuously, giving the plants the sustenance they need while avoiding over-watering.
Build the Hydroponic Unit
Drill a 1/2-inch hole in the bottom of the 10-gallon bin. Drill a 3/4-inch hole in the bottom of the 10-gallon bin. Position the holes near the center of the bin. It is not necessary to get the holes in the exact center, as long as they are not so close to each other that they compromise the structural integrity of the bin. Leave at least 3 to 4 inches between them.
Drill two holes--one 1/2-inch and one 3/4-inch--in the lid of the 20-gallon bin. Position these holes near the center, leaving 3 to 4 inches of space between them. As before, it is not necessary to get them in the exact center. Drill another 1/2-inch hole near the edge of the lid.
Install the drain fittings, following the manufacturer's instructions, in the holes you drilled in the 10-gallon bin. Remember to install the riser extension on the 3/4-inch drain fitting.
Place the submersible pump inside the 20-gallon bin and thread the power cord through the 1/2-inch hole near the edge of the lid. Loosely set the lid on the bin. Plug in the pump. You may need to run an extension cord if you don't have an outlet nearby.
Connect one end of the 1/2-inch tubing to the 1/2-inch drain fitting. Thread the other end through the 1/2-inch hole in the lid of the other bin and connect it to the pump. Use the knife to trim the tubing if necessary so that it does not coil.
Connect the 3/4-inch tubing to the other drain fitting. Thread the loose end of the tubing through the 3/4-inch hole in the lid. This tube will allow the nutrient solution to drain back into the reservoir.
Fill the larger bin--your nutrient reservoir--halfway with water. Turn on the pump and make sure that it fills the grow bed--the smaller bin--and that the water drains back into the reservoir through the drain tube. Drain the water out of the system and discard.
Add Your Plants
Fill the 10-gallon bin with HydroClay. Use the hose to saturate the HydroClay. Swirl it in the water to rinse off some of the dust, then drain the bin.
Plant your seedlings in the HydroClay, just as you would in regular soil.
Fill the nutrient reservoir with fresh water and allow it to sit, uncovered, for at least an hour. This will give the chlorine in the water a chance to dissipate.
Mix the concentrated nutrient solution into the nutrient reservoir according to the manufacturer's instructions. Place the lid securely on the reservoir, and set the 10-gallon grow bin directly on top of the reservoir. Make sure the tubing isn't being crushed by the grow bed.
Turn on the pump and let it run for 15 minutes to water the newly planted seedlings. Connect the timer to the pump and set it to turn on for 15 minutes every hour.