How to Create a Refugium and Its Benefits | Stabilizing Water Quality with Macroalgae and Seagrass | ブリちょく
Marine Fish| ✍️ BreederDirect Editorial
How to Create a Refugium and Its Benefits | Stabilizing Water Quality with Macroalgae and Seagrass
Learn how to set up a refugium (macroalgae tank) for saltwater aquariums and its benefits. We introduce the selection of macroalgae such as Chaetomorpha and sea grapes, lighting settings, and the effects of removing nitrates and phosphates.
Key Takeaways
Learn how to set up a refugium (macroalgae tank) for saltwater aquariums and its benefits. We introduce the selection of macroalgae such as Chaetomorpha and sea grapes, lighting settings, and the effects of removing nitrates and phosphates.
What is a Refugium? Its Role and Benefits
In saltwater fish and coral keeping, water quality stability is one of the most critical challenges. A refugium is a separate tank installed alongside the main aquarium, known as a "refuge and breeding tank," which is a system that biologically purifies water quality by cultivating macroalgae (large algae) and seagrass.
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A refugium has three main benefits. First, algae absorb nitrates and phosphates through photosynthesis, preventing eutrophication. Second, it serves as a cultivation ground for microfauna (microscopic organisms) such as copepods and amphipods, providing a stable food source for juvenile and small fish. Third, beneficial organisms proliferate in a predator-free environment, allowing for continuous supply to the main tank. A major strength is that the algae in a refugium continuously absorb organic matter over the long term that the Berlin system or protein skimmers alone cannot remove.
Equipment and Basic Setup Required for a Refugium
When setting up a refugium, first decide where to install it. There are generally three common patterns below.
Partitioned section within a sump (filter tank) is the most common approach. For tanks 90cm and larger, it is efficient to add a divider to the existing sump and reserve one section as a refugium. No plumbing work is needed, and circulation can be achieved with existing pumps.
Satellite-type (hang-on external installation) is designed for small tanks and is installed on the outside of tanks 60cm or smaller. While capacity is limited, it is space-efficient and easy to implement.
A dedicated stand-alone tank is the most effective approach, with a separate 30-60cm tank circulated with the main tank. While it requires more maintenance, it allows for abundant algae growth.
The required equipment is as follows.
Lighting: LED lights are sufficient. Models containing red and blue wavelengths are recommended. Running 18-24 hours promotes algae growth (opposite-phase lighting with the main tank can mitigate daily pH fluctuations)
Substrate: Using live sand (approximately 5-7cm) also provides denitrification benefits. Algae management is possible without substrate
Water flow: Gentle water flow is sufficient. Strong flow can damage algae
Circulation pump: Circulation should be approximately 3-5 turnovers of the main tank's total water volume per hour
Types and Characteristics of Major Macroalgae
Algae used in refugiums are selected based on purpose and ease of management.
Chaetomorpha is the most recommended species, with its entangled green algae efficiently absorbing nitrates and phosphates at high efficiency. It grows quickly and requires only thinning for management. Since it also serves as a habitat for copepods, it is excellent for microfauna cultivation.
Caulerpa (Caulerpa taxifolia / C. prolifera) grows extremely fast and has high removal effectiveness, but risks "collapse" during sexual reproduction, releasing large amounts of organic matter into the tank. Neglecting management can trigger collapse, making regular trimming essential. It should also be noted that Caulerpa species are regulated as invasive species in some regions.
Sea grapes (Caulerpa lentillifera) are also known as a food source and are hardy and easy to manage. However, nutrient absorption efficiency is lower than Chaetomorpha.
Seagrass (Halimeda, Thalassia, etc.) roots into the substrate and contributes to denitrification and substrate stabilization. While growth is slow, it provides stable purification benefits long-term.
Refugium Setup Procedure
Step 1: Confirm water circulation
First establish the circulation pathway with the main tank or sump. Measure whether flow rate is appropriate and adjust with a valve if necessary.
Step 2: Install substrate and live rock
Lay live sand approximately 5cm deep and place a few small pieces of live rock. These become the base for microorganisms.
Step 3: Introduce algae
Start with approximately 50-100g of Chaetomorpha (baseball-sized). With proper lighting and water flow, even small amounts will double in 2-4 weeks.
Step 4: Set up lighting
"Opposite-phase lighting," where the refugium light turns on when the main tank light turns off, is effective. This counteracts the pH rise from photosynthesis with the main tank's nighttime pH drop, keeping pH fluctuation within 0.1-0.2.
Step 5: Add copepods
Add commercially available copepod and amphipod sets to the refugium. In environments with abundant Chaetomorpha, they proliferate explosively, beginning natural supply to the main tank.
Maintenance and Nitrate Control Guidelines
Daily refugium maintenance primarily involves algae trimming. When Chaetomorpha doubles in volume, remove half. By discarding the removed algae, absorbed nitrates and phosphates are exported from the system. Neglecting this causes algae to deteriorate and collapse, worsening water quality.
The target nitrate level is 5ppm or less for coral-focused main tanks and 20ppm or less for fish-focused main tanks. When a refugium alone cannot keep up, concurrent use with a protein skimmer is standard. Many reports show that even in 60cm tank class setups, proper Chaetomorpha management can reduce monthly water changes by half.
Lighting maintenance is also important. LED output decreases after 2-3 years, so consider replacing the light if algae growth suddenly slows.
Common Failures and Solutions
Algae dissolving or turning brown: Insufficient light is the most common cause. Move the light closer or increase output. Next is decay from insufficient water flow. Eliminate stagnant areas in the refugium.
Nitrates not decreasing: The algae amount is likely insufficient. Ideally, 60-70% of refugium volume should be filled with algae. Also, neglecting to thin algae reduces absorption efficiency.
Copepods not increasing: If circulation between the main tank and refugium is too high, copepod proliferation cannot keep up with consumption by main tank fish. Reduce return flow to the refugium and create an environment where copepods can establish.
A refugium has low initial costs and can significantly reduce water change and additive costs long-term. For serious saltwater fish and coral keeping, it is a highly valuable system to consider implementing early.
