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Refugiums in Saltwater Aquariums


A refugium is nothing more than a refuge from predation. Sessile inverts, macroalgae and other delicate species need a place to call their own and the advent of the refugium was just the ticket! Isolated, but connected to the main display tank, the refugium allows for common water filtration while at the same time keeping more aggressive fish from impacting it. Refugiums have been found to be an excellent platform for cultivating food sources (amphipods, copepods and macroalgae) in a separate but still attached system.

Types of Refugiums

There are 3 types of refugiums: Hang-In-Tank, Hang-On-Tank and Sump (Under-Tank) style refugiums. Each type of refugium has its own pros and cons.

Hang-In-Tank Refugium

CPR CITR Hang-In-Tank Refugium
Photo by PriceGrabber
These refugiums can be the simplest and least expensive refugium to install in your tank. The DIY Hang-In-Tank Refugium is a great project if you want to build your own. You can also adapt the DIY Acrylic Refugium for Hang-In-Tank installation. Just drill holes in the refugium (below the waterline) and feed the refugium with tank water with a small powerhead.

Hang-In-Tank Refugium Pros & Cons

  • Pros: Doesn't require more room than you are already using for your tank; expensive refugium to install; easy to see what is in the refugium; uses existing tank lighting for macroalgae cultivation.
  • Cons: Can look sort of weird in the tank; doesn't add water volume to your aquarium system, limits timing of light schedule to that of your main aquarium.

Hang-On-Tank Refugiums

CPR AquaFuge 2 Hang-on Refugium
Photo by PriceGrabber

As it describes, Hang-On-Tank Refugiums hang on the tank (usually on the back of the tank, although you can install it on the sides or front, if you wish).

Hang-On-Tank Refugium Pros & Cons
  • Pros: Shares water with your main tank, which is essential if your are cultivating macroalgae to reduce nitrates and phosphates; doesn't "clutter your tank" like a hang-in-tank refugium does.
  • Cons: May require an additional light source; may be difficult to install behind your tank (due to wall clearance); may be difficult to clean due to position behind that tank.

Sump (Under-Tank) Refugiums

Precision Marine Regugiums
Photo by PriceGrabber
Is installed below the tank, usually in the tank cabinet. Sump refugiums are perfect for taking advantage of the new LED light fixtures now offered on the market. You can also take advantage of Cheap, Easy DIY Sumps and save money. Many sump refugiums have room for not only macroalgae, but separate spaces for return pumps and protein skimmers. If your tank is not drilled, you can install an Overflow Box Kit to move water from your main tank to your sump.

Sump (Under-Tank) Refugium Pros & Cons ;

  • Pros: Excellent platform for protein skimmers and other pieces of equipment; even if your tank isn't drilled, they can be fed from your main tank with an Overflow Box Kit add to total tank water volume; least expensive style refugium per water volume if Cheap, Easy DIY Sump is utilized; relatively inexpensive LED lighting fixtures work well with sump refugiums; plenty of room for growing Red and Green macroalgae.
  • Cons: Requires a separate light source; can be relatively expensive if a complete refugium system, with return pump and protein skimmer are included (see Top Refugiums for Saltwater Aquariums


No matter which refugium style you choose, adequate water flow to and from your main tank is required. Depending on what you are growing, a general "rule of thumb" is to turn the water over in your refugium at least once per hour. For amphipods and copepods, this should work well. If you are growing macroalgae, you might want to step it up to at least twice per hour as many macroalgae prefer a higher water movement in order to thrive.

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