Adding a refugium to your reef tank is one of the most effective ways to boost stability, nutrient export, and overall coral health. Whether you run a compact nano system or a large display, a well-planned refugium setup can help you grow macroalgae, support pods, and keep nuisance algae in the display under control.

What Is a Refugium and Why Use One?

A refugium is a dedicated area connected to your main reef tank where beneficial organisms and macroalgae can thrive with minimal disturbance from fish and high-flow equipment. It can be part of your sump, a hang-on-back unit, or a separate tank plumbed into the system.

Key benefits of a refugium setup for reef tanks include:

• Nutrient export: Macroalgae consume nitrate and phosphate, helping to prevent problem algae in the display.
• Pod production: Copepods and amphipods reproduce safely and provide a natural food source for fish and corals.
• pH stability: Running the refugium light on a reverse schedule can help balance daily pH swings.
• Increased biodiversity: Extra rock, sand, and algae create micro-habitats that benefit the entire system.

For an overview of how this fits into your overall filtration, check out our guide on sump setup for reef tanks.

Refugium Placement, Flow, and Lighting

The most common refugium location is in the sump, usually in the middle chamber between the skimmer and return pump. Hang-on-back refugiums are great for smaller tanks or systems without a sump.

Flow and Water Movement

• Aim for gentle to moderate flow so macroalgae can tumble slightly but not blast apart.
• Use a small powerhead if the area is too still, but avoid sandstorms that kick detritus everywhere.
• Adjust baffles or valves so the refugium gets a steady, consistent water level.

Lighting for Macroalgae Growth

Refugium lighting doesn’t need to be fancy, but it does need to be appropriate for plant growth. Many reefers use a compact LED grow light mounted above the refugium.

• Run the refugium light on a reverse photoperiod (on at night, off during display tank lights) to help stabilize pH.
• Start with 8–10 hours of light and adjust based on macroalgae growth and nutrient levels.
• Choose a spectrum designed for plants (often heavy in red/blue) for dense, healthy growth.

Macroalgae Choices and Maintenance Tips

For most reef tanks, Chaetomorpha is the go-to macroalgae: it grows fast, doesn’t attach to rock, and is easy to harvest. Other options like Caulerpa or red macros can work, but may require more attention.

Tip: Start with a small ball of Chaeto and monitor nutrients weekly. As it grows, you can harvest and discard or share with other hobbyists.

Basic Refugium Maintenance

• Harvest regularly: Trim macroalgae when it doubles in size; this is how you physically remove nutrients.
• Shake out detritus: Periodically swish macroalgae in old tank water during water changes to remove trapped debris.
• Clean the light: Wipe salt creep and splash from the light cover so PAR stays consistent.
• Test nutrients: Pair your refugium with a regular testing routine (see our reef tank water parameters guide) to avoid stripping nutrients too low.

As your refugium matures, you’ll likely see a surge in pods, more stable nutrients, and clearer water. Combined with good skimming and responsible feeding, this simple addition can transform the long-term health of your reef. For a full look at planning your system from the ground up, don’t miss our article on beginner reef tank setup.

With thoughtful placement, proper lighting, and consistent harvesting, a refugium becomes a quiet workhorse behind the scenes—keeping your display tank cleaner, more stable, and better suited for thriving corals and fish.