Sea Water Filteration

Filtration:

A new sump with three compartments including a protein skimmer

Main article: Filter (aquarium)

In general, marine aquariums have more complex filtration requirements than most freshwater aquariums. The various components frequently include wet and dry filters and protein skimmers. Protein skimmers are devices that remove organic compounds prior to their degradation, and are very useful in marine aquariums. Protein skimming is also used in the popular Berlin method that relies on live rock and periodic partial water changes to degrade and remove waste products. The Berlin method requires large amounts of live rock in the aquarium. The rule of thumb is 1/2–1 lb. per 1 US gallon (0.2–0.4 kg per 4 liters).
Some marine aquariums include a sump, which is an external container connected to the main aquarium with a water pump. In most setups, the sump is located below the aquarium and is fed water from the main tank via an overflow. An overflow at its simplest is a round hole drilled towards the top of the tank, connected via tubing to an output below it. As the water level increases past the height of the overflow, the water "overflows" the tank and falls through to the sump below. The water circulation is powered by a water pump in the sump, which pushes the water back into the tank, thus causing more water to flow over and perpetuating the cycle. There are many advantages to using a sump, both for the appearance and the health of the tank. The sump helps the appearance of the tank, because it allows filtration and maintenance equipment (protein skimmer, heater, activated carbon) to be kept out of sight of the main tank. It also ensures that the water level of the main aquarium never changes, as the overflow sets the water level in the main tank. The sump aids tank health by helping to oxygenate the water by increasing the amount of water/air surface area used for gas exchange.
Some marine aquariums also include a refugium. Refugiums are small containers or aquariums that are hidden behind or beneath the main aquarium and connected to it via a water pump (often in a similar manner to a sump). Refugiums have recently become quite popular among reef aquarists because they can be used to serve several purposes such as adding water volume or providing a fish-free site for biological filtration in live rock and/or the sandbed. Fish-free refugiums host populations of copepods, amphipods, isopods, and other zooplankton.