Figure 1.

Recirculating system (intermediate type). Reverse osmosis (RO) water flows from a holding tank into a reserve clean water sump tank (adjusted by a pH–salt doser), through 2- to 50-μm sock filters, is pumped to the top of the tank racks, exposed to UV light, into the fish tanks, out the tank baffle drains, through prefilter pads into the dirty water sump, from the dirty water sump into the fluidized sand filter, and finally back to the clean water sump. Engaging the flow-through switch or opening the valve allows some of the water to exit the filtration cycle at the dirty water sump through the overflow drain, where the water runs into the main sanitary sewer drain.