What is a refugium?

A refugium is a section of the aquarium sump where copepods, small worms and other benthic organisms are allowed to proliferate on small pieces of live rock, free from direct predation from fish.  The refugium is also where macroalgae, which aid in nutrient removal, can be grown.

What Is The Best Macroalgae For The Refugium?

Macroalgae works amazingly well at absorbing nitrates and phosphates from aquarium water.  Chaetomorpha is an extremely popular choice for refugiums as it is very hardy and doesn’t require a lot of light to keep it growing — a single 25 watt lightbulb is usually sufficient.


Refugium with macroalgae and sandbed

Resembling a wad of dark green, wiry fibres, chaetomorpha is free floating and doesn’t need to be attached to the substrate.  It requires only a small amount of water movement to prevent too much detritus from building up in it.  Colonies of copepods can be found thriving in masses of chaetomorpha, which is ideal as many eventually find their way into the main display tank via the return pump to provide a constant supply of food for the fish.

Chaetomorpha only needs to be pruned if it gets too large and dense and is done by simply pulling away handfuls of it and throwing it away.  You might be able to find a marine aquarium hobby club in your area where other hobbyists give away their excess chaetomorpha.

Caulerpa, on the other hand is a type of macroalgae that should generally be avoided.   Although it is just as efficient at nutrient control as chaetomorpha, it sometimes goes through a sexual reproduction phase where it releases spores, severely clouding the water and necessitating large water changes.

Refugium Lights

Macroalgae require light for photosynthesis, without which they will die.  Fortunately, the lighting requirements for macroalgae in a refugium are minimal — most will fluorish under a 25 watt lightbulb, preferably in the 6500k spectrum.

Although a more elegant solution would be to install a simple single T5 aquarium light fixture over the refugium, in the interest of preventing any possibility of electric shock due to moisture entering an exposed light bulb socket.

The refugium should be set on a reverse lighting schedule, opposite from the main display tank.  This will stablilize pH, preventing the usual scenario of plummeting pH levels when the lights go out in the main display.

Hang-On Refugiums

For sumpless tanks, a hang-on refugium is a good option.

Made from acrylic to minimize weight, a hang-on refugium requires a small pump to deliver water from the display tank.  The water then flows back passively into the display via another pipe.   A refugium light over the hang-on refugium is also required to keep the macroalgae happy.

Refugium Sandbeds

Some hobbyists add a 4″ to 6″ sandbed to their refugiums to further aid in nitrate removal. Refugium sandbeds seem to be less popular nowadays, mostly due to the fact that stray particles of fine sand inadvertently find their way into the return pump, which can damage the impeller.

Refugium sandbeds also tend to collect a lot of mulm and detritus  if they are not kept clean and vacuumed periodicaly.  Excessive buildup of mulm can actually contribute to nitrate buildup over time.

Read more about Saltwater Aquarium Setup:

What Is The Best Refugium Light?

Chaetomorpha | Best Macroalgae For The Refugium

Aquarium Tank Size | Length, Width And Height

The Ideal Location For Your Saltwater Aquarium In Your Home

Ready-Made Aquariums

Acrylic Aquariums

Custom-Built Glass Aquariums

Drilled Overflows Vs. Siphon Overflows

Aquarium Stands

Why Beginning Hobbyists Should Avoid Starting A Nano Aquarium

Aquarium Chillers

Aquarium Sump


Aquarium Covers | Put A Lid On It!

Cooling Fans


What You Don’t Need For Your Saltwater Aquarium!

Aquarium Sump As A Second Display Tank?

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