Refugium

Definition

A refugium is a separate aquarium chamber, typically in the sump, that grows macroalgae (chaetomorpha, caulerpa, gracilaria) under reverse-cycle lighting. The macroalgae consumes nitrate + phosphate as it grows, then gets harvested to export nutrients out of the tank.

Practical use in aquariums

Refugium lighting should run on opposite cycle to display lights to stabilize pH (CO2 absorbed by macroalgae during display lights-off prevents pH dip). 1-2 cups of chaeto per 50 gallons of system water is a starting point. Harvest one-third of the chaeto every 2-3 weeks.

How Refugium fits the bigger picture

Understanding Refugium matters because it's connected to broader husbandry decisions: equipment selection compounds: skimper + return + dosing all need to match each other and the tank size.

Browse the Fast Aquatics care library for full husbandry tutorials covering Refugium in context.