Aquarium Tips: Setting Up a Refugium

Article By Laurren Schmoyer of AquaticExperts.com

What is a Refugium?

When setting up your aquarium, it is highly recommended to create a refugium if you are using a Berlin sump for filtration.  A refugium is an additional chamber that is built into a saltwater, brackish, or freshwater fish tank that shares the same water supply. It is a separate sump, connected to the main display tank.  The name comes from the fact that it provides refuge for beneficial micro-organisms such as anaerobic denitrifying bacteria and photosynthesizers.

A built-in refugium is simply a compartment in a Berlin sump which houses mud or sand and algae. The walls of the compartment are designed to allow water to pass through, and then return the water to the display aquarium. These walls also slow water flow to assist with macro algae feeding.

How Large should the Refugium be?

The size of the refugium needed depends on the bio-load of the display aquarium. A larger refugium is necessary for a heavily stocked aquarium, while a smaller refugium may be used for a lightly stocked aquarium.  A good rule is 1:10 of the main tank volume.

What type of Lighting does the Refugium need?

Place a light over the refugium to help grow macro algae. The bulb should be 5,000 to 6,500 Kelvin for optimum plant growth. Choose a light fixture that produces at least 4 watts per gallon of water in the refugium (for those less than 16 inches deep).

Two T5 strip lights mounted above refugium

Set the refugium light to turn on when the aquarium light turns off.  This will keep the total system pH more stable, due to the constant uptake of carbon dioxide.  

What do I put in there?

Refugiums are easy to set up.  Just add mud and/or an oolithic (sugar size) aragonite sand to a depth of up to six inches and macro algae. Macro algae can be added to refugium 24 hours after aquarium is setup or you can wait until the aquarium has "cycled".  Chaetomorpha, Ulva (Sea Lettuce), Halimeda (red seaweed) and Gracilaria (red seaweed) are macro algae that do well in refugiums.

Berlin sump with refugium compartment with oolithic sand

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