Our aquaponic system established in Waedenswil, Zurich, was a new concept using lightexpanded clay aggregate (LECA TM) [13] as filter medium for the trickling filter. LECA is a type of clay, which is super-fired to create a porous medium. It is heavy enough to provide secure support for the plants’ root systems and was used in indoor and outdoor hydroponic systems [13–17]. LECA was filled in standard boxes (0.4 0.6 0.4m, green PVC), aligned in three rows in an adjoining greenhouse (Fig. 1). In total, 74 boxes were used, holding 3.0m3 of LECA.