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A refugium is one of the most valuable additions to a reef tank. It provides a protected space to grow macroalgae for nutrient export, cultivate copepods and amphipods for feeding mandarin dragonets and other finicky fish, and improve overall water quality stability.
What Is a Refugium?
- Macroalgae growth: Chaetomorpha and other macroalgae absorb nitrate and phosphate, providing natural nutrient export when harvested regularly.
- Copepod cultivation: A protected environment where copepods reproduce without predation - essential for mandarin dragonets and other copepod-dependent species.
- Water volume: Additional volume improves parameter stability in the display tank.
- Biological filtration: Live rock and macroalgae contribute to biological filtration.
Who Benefits Most from a Refugium?
A refugium is not required for every reef tank, but it offers major benefits for:
- Mandarin dragonets - essentially a requirement for long-term care
- Seahorses - same copepod dependency as mandarins
- Pipefish - same feeding requirements
- Reef tanks with persistent nitrate or phosphate issues - chaeto export is one of the most effective natural solutions
- Hobbyists wanting to culture copepods naturally for any finicky or planktivorous species
Types of Refugiums
Hang-On-Back (HOB) Refugiums
The most accessible option for tanks without a sump. Self-contained, easy to install, and effective for macroalgae growth and copepod cultivation in tanks up to 75 gallons.
Best for: Tanks without a sump, smaller reef setups, beginners adding a refugium for the first time.
Browse hang-on-back refugiums on Amazon
Sump-Based Refugiums
A dedicated compartment within the sump - the most common configuration in established reef tanks. Most effective for nutrient export and copepod cultivation at scale.
Best for: Tanks with an existing sump, larger reef setups, serious copepod cultivation for mandarin dragonets.
Browse reef sumps with refugium compartments on Amazon
Standalone Refugium Tanks
A separate tank connected to the display tank via a pump. Provides the most refugium volume and the best option for serious copepod cultivation.
Best for: Dedicated copepod cultivation for mandarin dragonets, large reef systems, advanced setups.
Browse refugium tanks on Amazon
What to Grow in a Refugium
Chaetomorpha (Chaeto)
The most popular refugium macroalgae and the best choice for nutrient export. Grows rapidly, easy to harvest, and does not go sexual the way some other macroalgae can. Harvest a portion every 2-4 weeks to export absorbed nitrate and phosphate. A neglected refugium filled with dying macroalgae will not provide the same benefits as one that is harvested and maintained regularly. Available from reef specialty retailers and online reef communities.
Caulerpa
Grows rapidly and is effective for nutrient export, but some species can go sexual and release toxins into the display tank. Chaeto is generally the safer and more recommended choice for most reef keepers.
Refugium Lighting
Macroalgae requires light to grow. A dedicated refugium light with a spectrum suited to macroalgae growth (6500K-10000K) is recommended. Running the refugium light on a reverse daylight cycle - on when display tank lights are off - helps stabilize pH by maintaining continuous photosynthesis.
Browse refugium lights on Amazon
Refugiums for Mandarin Dragonets
A refugium is essentially a requirement for keeping mandarin dragonets long-term. Mandarin dragonets feed almost exclusively on live copepods, and a display tank alone cannot sustain a sufficient population. A refugium provides a protected breeding ground that continuously seeds the display tank with live food. See our Mandarin Dragonet Care Guide.
How to Set Up a Refugium
- Choose your refugium type based on your tank setup
- Add live rock rubble for biological filtration and copepod habitat
- Add a chaeto starter culture from a reef retailer or reef community
- Add a copepod starter culture if cultivating pods for a mandarin or other finicky fish
- Install refugium lighting on a reverse daylight cycle
- Harvest chaeto regularly - remove a portion every 2-4 weeks to export nutrients