A refugium is a separate compartment or tank that provides natural filtration and nutrient export for saltwater aquariums. Typically located in a sump system, refugiums grow macroalgae, copepods, and other beneficial organisms that consume excess nutrients, provide natural food sources, and enhance overall tank stability. Setting up a refugium is one of the most effective ways to naturally control nitrates and phosphates while supporting a diverse ecosystem.
In this comprehensive guide, we've covered everything you need to know about setting up a refugium for your saltwater tank. We've explained how refugiums work, their benefits, setup procedures, equipment needed, macroalgae selection, maintenance, and best practices. We've also included product recommendations for refugium equipment, lighting, and macroalgae. All products reviewed here include direct Amazon purchase links with our affiliate tag.
What is a Refugium?
A refugium is a separate area (usually a chamber in a sump or separate tank) where beneficial organisms can grow without predation. The name comes from "refuge" - a safe place for copepods, amphipods, and other small organisms to reproduce and thrive.
How Refugiums Work
Refugiums work by:
- Growing macroalgae that consume nitrates and phosphates
- Providing habitat for beneficial copepods and amphipods
- Creating natural food sources for main tank inhabitants
- Enhancing biological diversity and stability
Benefits of Refugiums
- Natural Nutrient Export: Macroalgae consume excess nitrates and phosphates
- Food Production: Copepods and amphipods reproduce and flow to main tank
- Water Stability: Additional water volume and biological filtration
- pH Stabilization: Macroalgae photosynthesis helps maintain pH
- Natural Filtration: Biological diversity supports overall tank health
Refugium Setup Options
In-Sump Refugium
Most common setup. A dedicated chamber in your sump system, separated by baffles. Water flows from main tank through refugium before returning.
Pros: Integrated system, easy water flow, space efficient
Cons: Requires sump system, limited size
Key Features: Sump with refugium chamber, baffles, proper flow
View Sump Refugium Equipment on Amazon
Separate Refugium Tank
Dedicated tank plumbed into main system. Offers more space and flexibility but requires additional plumbing.
Pros: More space, better control, can be larger
Cons: Requires additional plumbing, more complex setup
Key Features: Separate tank, plumbing, flow control
Hang-On Refugium
Small refugium that hangs on back of tank. Good for smaller setups without sumps.
Pros: No sump needed, easy installation, good for small tanks
Cons: Limited size, less effective than larger refugiums
Key Features: Hang-on design, compact size, easy setup
View Hang-On Refugiums on Amazon
Essential Equipment
Refugium Lighting
Macroalgae need light to grow. Use LED lights with spectrum optimized for plant/algae growth. Run lights on opposite schedule from main tank (reverse photoperiod).
Key Features: Full-spectrum LED, appropriate wattage, reverse photoperiod capability
View Refugium Lights on Amazon
Substrate
Deep sand bed or mud provides habitat for beneficial organisms and additional biological filtration. 3-6 inches of fine sand or specialized refugium mud works well.
Key Features: Fine sand, refugium mud, deep sand bed
View Refugium Substrate on Amazon
Live Rock or Rubble
Provides additional surface area for beneficial bacteria and habitat for copepods. Use small pieces or rubble.
Key Features: Live rock rubble, porous structure, beneficial bacteria
View Live Rock Rubble on Amazon
Macroalgae
Chaetomorpha (Chaeto) is most popular. Other options include Caulerpa, Gracilaria, and Ulva. Choose based on your needs and tank conditions.
Key Features: Chaetomorpha, macroalgae starter, fast-growing species
Flow Control
Moderate flow through refugium is ideal. Too much flow prevents macroalgae from settling, too little allows detritus buildup.
Key Features: Flow control valve, appropriate flow rate, gentle circulation
Setting Up Your Refugium
Step 1: Design and Plan
Plan refugium size (typically 10-30% of main tank volume), location, and flow path. Ensure adequate space for macroalgae growth.
Step 2: Install Equipment
- Set up refugium chamber or tank
- Install substrate (3-6 inches deep)
- Add live rock rubble
- Install lighting
- Set up flow control
Step 3: Add Macroalgae
Start with small amount of macroalgae (Chaetomorpha recommended). Allow it to establish and begin growing before expecting nutrient export.
Key Features: Chaetomorpha starter, healthy macroalgae, proper introduction
View Macroalgae Starters on Amazon
Step 4: Establish Copepods
Introduce copepods and amphipods to refugium. They'll reproduce and provide natural food source for main tank.
Key Features: Copepod starter, amphipod culture, beneficial organisms
View Copepod Cultures on Amazon
Step 5: Set Lighting Schedule
Run refugium lights on reverse photoperiod (opposite main tank). This helps stabilize pH and provides continuous nutrient consumption.
Macroalgae Selection
Chaetomorpha (Chaeto)
Most popular choice. Fast-growing, doesn't go sexual, easy to harvest. Excellent nutrient export.
Best For: Most refugiums, beginners, reliable nutrient export
Caulerpa
Fast-growing but can go sexual and release nutrients. Requires careful management. Not recommended for beginners.
Best For: Experienced aquarists, aggressive nutrient export
Gracilaria
Edible macroalgae, slower growing. Good for refugiums and can be harvested for tangs.
Best For: Refugiums with tangs, slower growth preferred
Ulva
Fast-growing, good nutrient export. Can be harvested for tangs. Requires good flow.
Best For: High-flow refugiums, nutrient export, tang food
Maintenance and Care
Harvesting Macroalgae
Harvest 25-50% of macroalgae every 2-4 weeks. This removes nutrients and encourages new growth. Don't harvest all at once.
Trimming and Pruning
Trim macroalgae to prevent it from blocking flow or outgrowing refugium. Maintain manageable size.
Cleaning
Remove detritus buildup periodically. Gently stir sand bed to prevent anaerobic conditions. Clean glass if needed.
Monitoring Growth
Healthy macroalgae should grow steadily. Slow growth may indicate insufficient light, nutrients, or flow. Adjust as needed.
Key Features: Monitoring tools, test kits, growth tracking
Best Practices
Reverse Photoperiod
Run refugium lights opposite main tank lights. This stabilizes pH (macroalgae consume CO2 during day, release at night) and provides continuous nutrient consumption.
Adequate Flow
Moderate flow keeps macroalgae tumbling and prevents detritus buildup. Too much flow prevents growth, too little allows buildup.
Regular Harvesting
Harvest macroalgae regularly to remove nutrients. Don't let it overgrow or it may go sexual (Caulerpa) or block flow.
Copepod Production
Maintain healthy copepod population. They provide natural food and help control detritus. Avoid over-harvesting macroalgae that provides their habitat.
Common Mistakes to Avoid
Insufficient Lighting
Macroalgae need adequate light to grow and export nutrients. Underpowered lights result in poor growth and limited nutrient export.
Too Much or Too Little Flow
Balance flow carefully. Too much prevents macroalgae from establishing, too little allows detritus buildup and poor nutrient exchange.
Not Harvesting
Failing to harvest macroalgae means nutrients aren't being removed. Regular harvesting is essential for nutrient export.
Wrong Macroalgae Choice
Some macroalgae (like certain Caulerpa species) can go sexual and cause problems. Choose appropriate species for your experience level.
Final Verdict
Refugiums are powerful natural filtration systems that provide nutrient export, food production, and enhanced stability for saltwater aquariums. Setting up a refugium requires proper planning, appropriate equipment, and regular maintenance, but the benefits make them valuable additions to most saltwater systems.
Choose refugium type based on your setup: in-sump for integrated systems, separate tank for more space, or hang-on for smaller setups. Select appropriate macroalgae (Chaetomorpha recommended for beginners), provide adequate lighting and flow, and maintain through regular harvesting.
With proper setup and maintenance, refugiums will provide natural nutrient export, support copepod production, and enhance overall tank stability. They're particularly valuable for reef tanks and systems with high nutrient loads.
Use this guide as a reference when setting up your refugium, and don't hesitate to consult with experienced reef keepers or your local fish store for specific recommendations based on your tank setup and goals.