Macroalgae Care Guide for Refugiums & Reef Tanks
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Macroalgae pulls nitrate and phosphate out of the water, gives copepods and amphipods a place to breed, and adds color and movement to a refugium or planted marine display. Most species are easy to grow once they have light, nutrients, and steady flow. This guide covers general care, setting up a refugium, the species we grow, and how to fix the most common problems.
Water
Keep salinity stable at 1.024 to 1.026. Most macroalgae grows best in nutrient-rich aquarium water with moderate nitrate and phosphate. A tank with near-zero nutrients will starve it, so if you run very clean water, keep nitrate and phosphate at measurable levels rather than bottomed out.
Light
Provide 8 to 12 hours of moderate to strong light daily. In general, green macroalgae grows well under white or full-spectrum light, while red and blue species often develop deeper color under blue-heavy reef lighting.
Water flow
Moderate water movement keeps detritus from settling on the algae and supports healthy growth. Too little flow lets debris and nuisance algae coat the fronds.
Temperature
Keep typical reef temperatures of 72 to 80°F.
Placement
Some species, such as Caulerpa and Ochtodes, attach to rock or substrate. Others, such as Codium, Gracilaria, and Dragon's Breath, can be placed loosely or tucked into rockwork for display.
Setting up a refugium
A refugium is a separate, lit chamber, usually in the sump, where macroalgae can grow without being grazed. A few tips:
- Lighting schedule: many reefers run the refugium light while the display light is off. Photosynthesis in the refugium at night helps keep pH more stable around the clock.
- Flow: aim for gentle, steady flow through the chamber. Fast-growing species like Red Ogo do especially well when they're kept tumbling.
- Harvest: trim regularly once growth takes off. Every bit you remove exports the nutrients it absorbed.
Species we grow
- Codium "Dead Man's Fingers" is a hardy green macro with thick, velvety branches. It's a good all-around choice for refugiums and displays, also available attached to live rock and in bulk.
- Caulerpa lentillifera "Green Sea Grape" is one of the fastest nutrient exporters available, with bead-like fronds that spread by runners.
- Gracilaria "Red Ogo" is a fast-growing red macro that grazing fish love, and a great choice for refugiums and feeding.
- Halymenia "Dragon's Breath" is a showy red macro with flowing branches that glow orange-red under reef lighting.
- Blue Ochtodes is a red macroalgae with striking blue-violet iridescence. It is a slower-growing display piece that attaches to rock.
Troubleshooting
Melting, fading, or turning white
Usually caused by a sudden change in light, salinity, or temperature, or by nutrients dropping to zero. Check your parameters, keep conditions stable, and remove any dying pieces quickly so they don't foul the water.
Caulerpa "going sexual"
Caulerpa can suddenly turn pale or clear as it releases its contents into the water, often after stress or a sudden change. Remove the affected algae right away and do a water change. Regular harvesting and stable conditions help prevent it.
Covered in hair algae or cyanobacteria
Nuisance algae growing on your macro usually means low flow or excess nutrients the macro can't keep up with. Increase flow, rinse the macro gently in tank water, and harvest more often.
Not growing
Check light first, then nutrients. Macroalgae can't grow in water with no measurable nitrate or phosphate.
A responsible note: never release macroalgae into local waterways or drains. Some species can become invasive.
FAQ
Why is my macroalgae melting or turning white?
Common causes are a sudden change in light, salinity, or temperature, or nutrients dropping to near zero. Caulerpa can also "go sexual," turning pale or clear as it releases its contents into the water. Remove any affected algae quickly and do a water change.
Which macroalgae is best for nutrient export?
Fast growers like Caulerpa and Red Ogo (Gracilaria) pull the most nitrate and phosphate. Slower, showier species like Blue Ochtodes and Dragon's Breath are grown more for display.
Will my fish eat macroalgae?
Tangs, rabbitfish, and some angelfish graze on macroalgae, and Red Ogo is a favorite food. Keep display species in a refugium if you have heavy grazers.
How often should I trim macroalgae?
Harvest regularly once it's growing well. Every bit you remove takes the nutrients it absorbed out of the system, and trimming keeps it from shading itself out.