Fluidized bed filters have been developed in aquaculture institutions to cope with the high density of fish. Although their design options, the concept is quite simple. Acrylic or PVC tube filled with fine sand. It usually hangs on the back of an aquarium or sump or is self contained inside a pan. The pipe is either sealed at the bottom or at both ends to form a pressure chamber. Water is pumped to the bottom of the tube, squeezed through the sand and out of the outlet at the top of the tube. Sand granules provide an intensive amount of surface area for the colonization of nitrifying bacteria. As the grains of sand and water spin in the tube, the bacteria feed and some are cleaned from the surface of the sand. This ensures that new nitrifying bacteria are constantly growing on the surface of the sand. Young fast-growing colonies of nitrifying bacteria turn waste into nitrates much more efficiently. Continuous grinding of the sand ensures the preservation of bacteria in a state of exponential growth. These filters have proven their value for public aquariums or central water systems with high generation of wastes with a high density of fish. Dangerously high ammonia levels will be reduced to unreadable levels within a few hours when a fluidized bed filter is added. Fluidized bed filters have become very popular with home aquarists lately, although for aquarium hobbies they are very different from the huge units used in commercial aquaculture.
Activated carbon is created by exposing carbon grains to high temperatures and pressures, which results in very porous materials that function in the same way as a sponge. Activated carbon works in two ways to remove organic molecules from the water column. It captures organic compounds in the pores and chemically binds polar organic molecules to the surface of carbon grains. Activated carbon can be used in various ways depending on the type of installation used and the available room. The best results occur when water is supplied through carbon, so no water can bypass it. Carbon can be placed in mesh bags and placed under the water inlet in a sump or in an integrated chamber. Built-in chambers can be made of PVC pipe, equipped with gearboxes and tubing pipes, and provided with foam at the inlet and at the outlet to hold the carbon in place. The canister filters can also be filled with activated carbon and installed on the sump. Bags of carbon that simply fit in the sump will absorb organic molecules, albeit much more slowly.
