They tested the following designs: gravel systems flooded with water, systems using the nutrient
film technique in which plant roots were exposed to air and roots were bathed with a thin layer of
fish water, and raft systems. They found that the gravel systems flooded with water were the
best. Ako (2013) tested trickling water under gravel, gravel ebb and flow, rafts with air gaps, and
standard rafts. He found the first two to be best, but the former to be more maintenance free