How to Set Up a Refugium with Macroalgae

A Simple Guide to Boosting Water Quality Naturally

A refugium is one of the best upgrades you can make to your saltwater aquarium and adding macroalgae is a game-changer for nutrient export, biological balance, and overall tank health.  In this post, we’ll walk you through everything you need to know to set up a refugium with macroalgae, whether you’re just starting out or looking to optimize your current system.

What Is a Refugium?

A refugium is a dedicated space in your aquarium system (usually in the sump) where beneficial organisms and plants can grow without being disturbed by fish or high flow. It serves as:

• A natural filter for removing nitrates and phosphates
• A safe space to grow copepods and amphipods
  
• A place to grow macroalgae like Chaetomorpha and Caulerpa
  

Think of it as a mini-ecosystem that supports the health and stability of your main display tank.

Why Use Macroalgae in Your Refugium?

Macroalgae is the heart of most refugiums. It:

• Absorbs excess nutrients (nitrate & phosphate)
• Helps prevent nuisance algae in your display tank
  
• Increases oxygen levels through photosynthesis
  
• Provides habitat for microfauna
  
• Is easy to grow and maintain
  

Popular choices include:

• Chaetomorpha (Chaeto) - fast-growing, doesn’t attach to surfaces
• Caulerpa - powerful nutrient exporter (but can go sexual, so trim regularly)
  
• Gracilaria - also doubles as tang food
  

How to Set Up a Refugium with Macroalgae

1. Choose Your Refugium Location

• In-sump refugiums are most common - usually in the middle or end chamber
• Hang-on-back refugiums are great for smaller tanks
  
• Display refugiums are visible and great for showing off macroalgae
  

2. Add a Substrate (Optional)

You can run a bare-bottom refugium or add:

• Live sand - to support bacteria and microfauna
• Rubble rock - for added surface area and pod habitat
  

3. Provide the Right Lighting

Macroalgae needs strong, full-spectrum light (especially in the red and blue range). Look for:

• Refugium-specific LED lights
• Grow lights (like the Kessil H80, AI Fuge, or Tunze 8831)
  
• Photoperiod: 8 - 12 hours per day (some run reverse lighting to stabilize pH)
  

4. Add Macroalgae

Start with a clean, pest-free batch of macroalgae (like those we ship from The Algae Plug).

• Rinse in clean saltwater
• Place loosely in the refugium - don’t pack it too tightly
  
• Use a tumbler if needed to keep it rotating gently and evenly lit
  

5. Maintain Proper Flow

Too much flow can damage delicate algae; too little can cause detritus buildup.

• Aim for moderate flow that keeps the algae gently moving
• Use a small powerhead if needed
  

Ongoing Refugium Maintenance

To keep your refugium thriving:

• Harvest macroalgae regularly to remove absorbed nutrients
• Clean out detritus buildup in the substrate
  
• Trim and monitor fast-growing algae like Caulerpa to prevent die-off
  
• Check lighting and replace bulbs/LEDs as needed for growth
  

Bonus: Stock It with Copepods

Your refugium can also be a pod hotel. Add copepods and amphipods to create a breeding ground for beneficial microfauna. They’ll naturally migrate to your display tank and feed corals and fish.

Final Thoughts

A refugium with macroalgae is a powerful, low-maintenance way to:

• Improve water quality
• Stabilize nutrient levels
  
• Support biodiversity
  
• And make your reef tank more resilient over time
  

At The Algae Plug, we ship clean, healthy macroalgae across Canada, ready to help your refugium thrive.