Moving bed bio filter. This is the biological filtration for the koi pond. It purifies water from ammonia and nitrites before it is sent back to the pond. The pump in the picture is the most efficient variable speed axial flow pump there is, Flow Friend pump. It uses fraction of power of typical pond water pump and produces multiple HP. Purified water distributed through custom outlet manifolds, the largest one on top goes to another bio filtration (bakki shower) to further purification, while the rest goes back to the pond.