Aquaponics is the ultimate form of food production. It grows fish in tanks and then uses the fish waste to feed plants. The plants clean the water for the fish, and the fish feed the plants. This technique has been in use from Asia to the Americas for thousands of years.
Closed loop aquaponics is the name for the method where you’re trying to recycle all the fish waste and not need to add any more nutrients for the plants. This can be a challenge because you have to balance the right number of fish with the right number of plants.
There are three main techniques for how to grow plants using closed loop aquaponics. The plants need access to the water. The fish and the plants both need access to oxygen. And both the fish and the plants need the appropriate amounts of both oxygen and water.
First, there is the nutrient film technique which is popular with crops like strawberries. A constant stream of nutritious water flows over the roots of the plants. The agitation of the flowing water also oxygenates it for both the fish and the plants. This is great for small plants but requires constant power to pump the water.
Second is the ebb/flow technique. Roots need both air and water in order to grow and thrive. Too much of one of the other can harm the plants. This technique solves this problem by using a bed just like the other botanical cells. The difference here is that there is no soil. The bed is filled with gravel or clay pebbles. The bed is then constantly flooded and drained in order to oxygenate the water and the roots. There are advantages and disadvantages to this technique. You can grow bigger plants more easily using this technique. It’s probably the only one of these techniques that would work well for something like a fruit tree for example. However it does require constant power in order to work, and a power failure could harm both the plants and the fish.
Third (and my favorite) is the deep tissue technique. This is based on ancient traditions from Thailand to Mexico City, where floating rafts are seeded with crops that then grow directly into the water, absorbing nutrients and protecting the water from evaporating. Today we use styrofoam sheets as the rafts with holes cut for small net pots that the seedlings can grow in. The water is oxygenated by using a waterfall or agitator to introduce oxygen into the water. This oxygen is needed by both the fish and the root systems. This technique requires no power, which also has the added advantage that losing power does not harm your plants.
In a twist on the first two techniques, there is a hybrid technique called the Dutch Bucket Method. This method is very popular for tomato cultivation. The tomato plants grow in a net pot in the lid of a bucket. A tube constantly drips water into the net pot. Then the roots simply reach down into the empty bucket, and the dripping water rides the roots down to the bottom of the bucket, where the water drains through a spout into a return pipe that takes the water back to the fish tank.