I wanted to build a system that was more eco-friendly than barrelponics, that was also small, portable, aesthetically pleasing and easy to set up and maintain. Here is a modernized version, often called a "lettuce raft" design. I love the lettuce raft, since this design demonstrates that modern aquaponic gardening can be very simple, and as my mother-in-law often says, "The simpler the better."
Many aquaponic gardeners start with Deep Water Culture, or "DWC" for this reason. Remember the Aztecs floating rafts, or "chinampas"? That was their way to garden with DWC. I modified the "DWC" design using a ten gallon glass aquarium, to reduce the amount of plastic, and used a wooden platform instead of a floating styrofoam raft.
Heres how it works:
As you can see, the plant roots are in direct contact with the water, and an airstone provides the oxygen source that the plants need to grow. Visually, its easy to understand whats happening. Plus, it is easy to make. Another benefit to floating rafts is that it is very low maintenance. The water level can fluctuate but the roots always stay wet. One could put an automated timer above the fish tank and go on vacation for a week without worrying too much about system failure.
I considered more affordable options. For instance, styrofoam (polystrene) is used in commercial aquaponic systems, so isnt it safe to use?
Well, thats debatable. Polystyrene is considered a "stable" plastic and widely used in the food industry - from tupperware and Saran Wrap to plastic utensils. But just because we use it doesnt mean that its necessarily good for us, right?
I discovered that the Dow "blue board" styrofoam insulation (available in local hardware stores) contains a highly toxic flame retardant and other toxic chemicals that are banned in many countries. I believe that the Owens Corning "pink board" does as well; of course, these products arent intended for Aquaponics use. Over time, the polystrene breaks down with sunlight exposure, and if fish ingest the foam, they wont be able to pass it through their digestive system.
Bamboo floats well, and seems like a much safer alternative. Unfortunately bamboo is expensive and sheets of bamboo are not easy to find. So, I created a wooden platform over the tank instead with 1/2" pine plywood, and drilled big holes in it to support cups for the hanging plants. With holes in the bottom of plastic cups, the plant roots can grow into the nutrient-rich water. I added some gravel, and planted some lettuce. Since it doesnt float, the water level has to be monitored a bit more often, so that the bottom of the hanging cup makes contact with the water.
One major benefit to a wooden platform is that it completely blocks out sunlight from entering through the top, preventing algae growth. Algae will kill the lettuce roots. I surrounded three sides of the tank with a black garbage bag to keep direct sunlight out, and can still view the fish from the open side.
Heres a close-up of the top of the tank with a few baby lettuce.
A vital aspect of DWC is providing oxygen directly to the plant roots with an airstone or bubble wand. Many aquarium hobbyists avoid airstones to oxygenate the water as they create too much back pressure on the diaphram of the air pump which shortens the life of the pump.
So, I made a "bubble wand" out of 1/4" airline tubing instead, and poked holes in the tubing with a thumb tack. Its held down with suction cups made to hold airline tubing. Now I have a constant stream of bubbles providing oxygen to the plant roots. Plus, I shaved $5 off the cost of the system. Sweet!
What about the fish? Dont they need some sort of biological filtration, too?
Technically, no. But providing additional filtration is a good idea, as it makes the system easier to maintain, overall. Sponge filters create surface area for the "good" bacteria to grow, which is especially useful when the lettuce roots are small and getting established.
I made a sponge filter using the bottom half of a water bottle, an aquarium foam sponge, 8" of 1/2" pvc pipe and some gravel, and connected it to the bubble wand with a "T" adapter, some airline tubing and a two-way aquarium airvalve to control air flow between the bubble wand and sponge filter.
Heres another side-view of the tank showing sponge filter (right), and the bubble wand (middle).
Basically, I followed the design from this Youtube video and added gravel in the bottom to keep the filter from floating away.
The water stays nice and clear. Another benefit of having a sponge filter is that it agitates the surface of the water, which is good for both the fish and plants. Its safe for a variety of fish in all kinds of aquariums, especially baby fish, slow swimming fish, shrimp or crayfish tanks because you dont have to worry about them getting sucked into the filter.
So far, so good. The lettuce is growing, and the goldfish seem happy. The air pump only uses 2 watts of power to power the bubble wand and the sponge filter, so its an inexpensive system to operate.
Feel free to contact me with any questions and I hope to see you at my upcoming "Introduction to Aquaponics" workshop on Wednesday, May 15 at the Putney Library. Its free!
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