When you get into the reef aquarium world, you will soon find out more about sumps, filters and refugiums. These are open reservoirs of water that are held below reef aquariums, which collect water from the surface. The water is then pushed back into the reef tank with a pump, which may also include a filtration system that helps to clean and improve the condition of the water. These are necessary components of reef tanks, and there are some different options to choose from. Reef aquarium sumps come in three varieties - Berlin reservoirs, wet-dry filters and refugiums. The Berlin sump is different from other sumps for reef aquariums, which have sections that contain pumps or intakes. The Berlin sump includes a completely open reservoir, though, which is fed water from the surface of the reef tank but still requires an overflow pre-filter like other systems.
A refugium is a sump for reef tanks that includes a partitioned area to help grow marine plants that absorb the nitrates in the water. These nitrates act as fertilizer for the reef aquarium plants, and keep the nitrate level in the reef aquariums at zero or very close to it. A refugium can be a second sump system added to the reef tank, or it can be the main sump system with a partitioned area for the main pump, a lit area for the marine algae, and another area for a protein skimmer. In general, all of these are fine options, but reef tanks that only have fish and no live rock are typically better with wet-dry filtration systems.
