There are three different types of aquaponics systems that have been developed for use by home gardeners and commercial enterprises. These are media based, NFT and Deep Flow or Raft systems and here is a description of each one.
Media-based: also known as the gravel bed system, the media-based aquaponics system is the simplest type to set up and can be used on a small or large scale. This is why it is the type most commonly used by backyard aquaponics enthusiasts. Containers are filled with small rocks, usually expanded clay pebbles which are porous to absorb water and air, and then seedlings are planted directly into these. Water from the fish tank is circulated through the container to allow the plants to access the nutrients. The rocks act as a biological filter as well as a solids filter, eliminating the need for extra equipment.
You can also use special netted growing pots for your seeds or seedlings. You fill these with perlite, coir, peat moss or the clay pebbles and plant into them. These pots are then placed into a larger container which has been filled with the expanding clay pebbles, making sure the netted sides are covered by the media. Media-based aquaponics systems hold plants firmly and so are ideal for growing fruiting plants.
There are two different ways this type of aquaponics system can be operated. The first method pumps a continuous flow of water through the media bed from the fish tank and back into the tank. The second is a process called flood and drain or ebb and flow, where water is pumped into the bed to a depth of about 10 to 12 inches (20 to 30 cms) and then drained away. A timer controls the flooding and draining sequence.
NFT system: or Nutrient Film Technique is a common method used in hydroponics that is best suited to a large-scale aquaponics production. This is because of the expense of setting up the system of PVC pipes and mechanical filtration needed to operate the system. Because there is not the surface area exposed to the air, as in the media-based system, a biological filter is needed to allow the beneficial bacteria to develop and convert the fish wastes into plant nutrients. Solids filtration is also needed to deal with the solids in the fish waste; this is usually set up in a separate tank through which the water passes before going through the plant pipes.
In the NFT system, plants are held in netted growing pots which are suspended through holes cut in the pipe. A thin film of nutrient-rich water is run along the bottom of enclosed gutters so that the roots can reach it. It is really only suited to plants that have a small root systems, such as leafy green vegetables.
Deep Flow: also called Deep Water Culture (DWC) or the Raft system, this is another commonly-used method in hydroponics. This system involves the use of a foam ‘raft’ that floats on top of the water. It is a popular choice for both commercial and backyard aquaponics because it is relatively cheap to set up and operate.
A container or channel is used to hold the water as it is pumped through from the fish tank, after it has been filtered to remove any solid waste. Plants are held in holes made in the raft, so their roots dangle down into the water. This method uses high volumes of water which provides stable water temperatures for the plants and fish. It is the method most often used in commercial aquaponics operations because of the ease with which the plants can be tended and harvested. Again, it is better suited to growing herbs and leafy green vegetables than plants with bigger root systems and fruiting varieties.
This type of system can easily be adapted for home garden use by simply floating a styrofoam tray on top of a fish tank. Just cut holes in the tray and suspend the plants, or plants in netting pots, through the holes so the roots are in contact with the water. Choose fish varieties that are not voracious plant eaters to avoid having plants’ roots eaten away.
Now that you understand how each of the 3 types of aquaponics systems operates, you will be in a better position to decide which one suits you the best. Whichever method you choose, it is best to start small so you can gradually build your expertise and experience before setting up a large system.
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