Refugium (fishkeeping)

In fishkeeping, a refugium is an appendage to a marine, brackish, or freshwater fish tank that shares the same water supply.

[1] It is a "refugium" in the sense that it permits organisms to be maintained that would not survive in the main system, whether food animals, anaerobic denitrifying bacteria, or photosynthesizers.

[2] To achieve maximum biological filtration through uptake of nutrients by macroalgae/mangroves, strong lighting is often utilized in the refugium.

In addition to housing critical equipment, the sump serves to add volume to the total system; mitigating the effects of nutrient buildup or unintentional introduction of foreign substances.

In home aquariums, the refugium is typically located in the cabinet underneath the main tank.