A primary goal of the system was to test a completely closed RAS, making use of fish faeces, too. The raw effluent from the 2.5m3 fish tank (2 2m square, water depth 0.65 m,green fibre glass with central outlet at the bottom) was pumped and distributed in the LECA filter at a rate of 10–15m3 h1 with a specially developed irrigation system. To achieve a homogenous load of Total Suspended Solids (TSS) distribution to the plant boxes, standard sewage piping (d = 0.11 m, orange PVC) was levelled horizontally over the LECA rows and each box irrigated through a drilling hole of 6 cm diameter.
The water exchange rate was set to zero, and the system was operated as a closed looped
system. Only evaporation water was replaced with tap water. Technical details were described only in an unpublished report so far [18].