There are three main types of hydroponic techniques that are currently employed, Media Bed, Deep Water or Raft, and NFT (Nutrient Film Technique). Each type has a variety of configurations that can be employed, but almost all Aquaponic systems are essentially based on one or a combination of these three types.
This type of Aquaponics is the most user friendly, as there are no additional filter components needed and the waste water is delivered to the media bed directly, where the solids and nutrient solution are allowed to permeate the media and plants roots and then return to the fish tank.
Media beds are commonly filled with an inert media such as expanded clay pellets or gravel and are 6" to 12" deep. There is a selection of sizes available including 2' x 2', 2x4, 3x3, 3x6, 2x4, 4x4, 4x8 and other sizes. The media used should be inert as the composition may affect the water quality by leaching materials into the system. Worms are also use to assist in breaking down the solids that are deposited into the bed. The media is also the source of surface area for bacterial colonization and is usually sufficient for nitrogen conversion.
N.F.T. (Nutrient Film Technique)
NFT is a hydroponic technique that delivers a thin film of nutrient solution down the bottom of a channel, where the plant roots spread out and filter the nutrients from the water. The thin film of solution allows the rest of the channel to be open to the air, which enables a high amount of oxygen availability for the roots. The channels or gutters have plants spaced according to size and do not require any media for the plants roots.
This reduces to initial and future cost of supplies and plants are usually started in a rooting plug, where they are grown for a few weeks until sufficient root mass has developed and they are transplanted into the NFT channels. Since the water delivery lines are usually of a small diameter, they have a high susceptibility to clogging from debris and additional solids removal is needed to ensure the delivery of solution to the plant roots. Since there is no media for plant support or bacterial colonization, additional bio filtration and support may be needed.
Deep Water Culture or Raft
In deep water culture, plants roots are submerged in a highly oxygenated nutrient solution and little to no media is used. These systems require additional solids removal to prevent buildup. Depending on the size of the system, the surface area of the tanks and rafts used is usually sufficient for bacterial colonization and nitrogen conversion.
Raft style Aquaponics was pioneered by the University of the Virgin Islands and is composed of tanks for the fish, a solids removal clarifier, a mechanical filter, degassing chamber, hydroponic rafts and a sump/base addition tank. The hydroponic troughs are typically 1' deep by 4' wide and can be up to 100' long.
Styrofoam sheets are floated on top of the filled troughs and plants are placed in net pots in the sheets and the roots are allowed to hang suspended in the nutrient solution. Since the roots are completely submerged, oxygenation is critical and air stones are placed every 2'-3' down the channel. Also due to the lack of media for anchorage, only smaller plants are used unless some sort of support is added. Young plants are placed in the properly spaced holes in the beginning of the channel and harvested out of the end so that the Styrofoam sheets can be floated down and another one placed in at the start.