It is a mostly aquaponic method that is normally used in closed circuits of controlled, self-sustaining systems of crops. It consists of a layer of porous material such as the perlilla that facilitates the filtering function of the water circulating in aquaponic crops, and serves as a means for the decomposition of waste, which is why they are commonly equipped with worms that optimize their function.
- It optimizes the filtering function: bio-filtering and macro filtering, due to its high level of porosity and the presence of living organisms added for this purpose.
- It allows the transformation of toxic ammonium into non-toxic nitrates.
- It favors a fast and healthy growth of the plant.
- It is an excellent substrate for optimal root growth.
The disadvantages are mainly economic and practical when it comes to a proper configuration of the assembly, since it requires that the water level, and its flow, be constant in the middle bed, which requires adaptations in the water supply pump and possibly increase the energy consumption. (Source: http://www.backyardaquaponics.com/guide-to-aquaponics/running-system/).