This publication describes how to construct and operate such a system. We had eight trays in the experimental set-up shown in the photos, but one tray, or any number, can be used. The only electrical component in the system was an air pump to aerate the fish tanks, providing the fish with oxygen and preventing denitrification. A list of materials and supplies used in this experimental set-up, their costs when purchased in 2008, and the vendors they were acquired from is given on p. 6–7.