Most commercial aquaponics units are raft systems.
This is largely due to the long standing influence of the UVI Aquaponics Research Center, and the success of their model.
Raft systems are somewhat under represented at the backyard level – particularly in Australia – probably due to early promotion of the Speraneo-style flood and drain model.
Raft aquaponics is essentially the same as the CHOP system but, instead of media-based flood and drain grow beds, raft tanks or troughs are used to grow plants.
The other essential difference is that raft systems invariably feature mechanical filtration. Even aquaponics fundamentalists, who might argue (albeit unconvincingly) that particulate waste can remain in a flood and drain system, acknowledge the need for mechanical filtration in raft systems.
For practical purposes, water flows from the fish tanks through filters and into grow tanks or troughs which contain Styrofoam rafts. The rafts support the plants.
The water flows from the grow tanks into a sump tank. A pump located in the sump tank moves the water back to the fish tank.
The water in the raft system recirculates continuously.
The Aquaponics Research Centre located at the University of Virgin Islands (which has been operating for over 25 years) is arguably the most widely recognised aquaponics system in the world and serves as the model for most raft systems.
The advantages of the raft system include:
Its stability – the relative volume of water in a raft system ensures that it is more stable (in terms of water quality and temperature) than flood and drain systems of a comparable size.
Easier to operate – little testing required and minimal daily maintenance.
The existence of a large body of research data.
Cheaper to build than flood and drain systems of comparable size – small sump tank.
Higher productivity than flood and drain systems of a comparable growing surface area.
Portability – small backyard systems can be emptied and moved relatively easily.
Raft tanks can be built from timber, plywood, cement blocks, pre-cast concrete sections, fibreglass or (for smaller systems) plastic.
The plants are inserted into holes cut into the Styrofoam rafts. The hole spacing will vary according to the type of plant to be grown.
Raft systems are ideal for the production of Asian greens, salad leaf vegetables and soft herbs, however, they have also been used to grow many other vegetables – particularly tomatoes.
It’s likely that raft aquaponics will become more common at the backyard level as people become better educated about its benefits.