Types of aquaponics

Raft/Deep Water Culture (DWC)

In a raft system (also known as float, deep channel and deep flow) the plants are grown on Polystyrene boards (rafts) that float on top of water allowing the roots to hang down into the water. This can be done in a number of ways. This method is one of the more commonly practiced commercial methods. This can be done by floating a foam raft on top of the fish tank, however, most often, this is in a tank separate from the fish tank, that is to grow the fish in a fish tank and pump the water through a filtration system, and then into long channels where floating rafts filled with plants float on the water surface and extract the nutrients and then back to the fish tank. The beneficial bacteria live in the raft tank and throughout the system. The extra volume of water in the raft tank provides a buffer for the fish, reducing stress and potential water quality problems. This is one of the greatest benefits of the raft system. In addition, the University of the Virgin Islands and other research programs refined this method during 25 years of research.  In a commercial system, the raft tanks can cover large areas, best utilizing the floor space in a greenhouse. Plant seedlings are transplanted on one end of the raft tank. The rafts are pushed forward on the surface of the water over time and then the mature plants are harvested at the other end of the raft. Once a raft is harvested, it can be replanted with seedlings and set into place on the opposite end. The optimizes floor space, which is especially important in a commercial greenhouse setting.

Nutrient Film Technique (NFT)

NFT (Nutrient Film Technique)  is a commonly used hydroponic method which the plants are grown in long narrow channels.  In NFT systems, nutrient rich water is pumped down small enclosed gutters, the water flowing down the gutter is only a very thin film. Plants sit in small plastic cups allowing their roots to access the water and absorb the nutrients. A thin film of water continuously flows down each channel, providing the plant roots with water, nutrients and oxygen. As with the raft system, water flows continuously from the fish tank, through filtration components, through the NFT channels where the plants are grown and then back to the fish tank. In NFT, a separate bio filter is required, however, because there is not a large amount of water or surface for the beneficial bacteria to live. In addition, the plumbing used in a hydroponic NFT system is usually not large enough to be used in aquaponcis because the organic nature of the system and "living" water will cause clogging of small pipes and tubes. NFT aquaponics shows potential but, at this time, it is used less than the other two methods discussed here. NFT is only really suitable for certain types of plants, generally leafy green vegetables, larger plants will have root systems that are too big and invasive, or they become too heavy for the lightweight growing gutters.

Media-filled bed

A media-filled bed system uses a tank or container that is filled with hydroton, gravel, perlite or another media for the plant bed. This bed is periodically flooded with water pumped from the fish tank and palnts grow in the hydroton or gravel media. The water then drains back to the fish tank. All waste, including the solids, is broken down within the plant bed. Sometimes worms are added to the gravel-filled plant bed to enhance the break-down of the waste. This style of system can be run two different ways, with a continuous flow of water over the rocks, or by flooding and draining the grow bed, in a flood and drain or ebb and flow cycle. This method uses the fewest components and no additional filtration, making it simple to operate. The production is, however, much lower than the two methods described above. The media-filled bed is often used for hobby applications where maximizing production is not a goal.