You may have seen them: saltwater aquariums that come with another tank underneath, usually neatly hidden behind closed cabinet doors. Sometimes the second container holds only equipment, which is known as a sump. Other times, though, it contains a veritable little ecosystem: a refugium.
Should your aquarium have a “Mini-me”? We think that if you’ve got the space, you’ll love the added convenience of a refugium. Here’s why we’re fans of refugia and how to install your own!
All the cool kids have a refugium
A refugium, in ecology, refers to a location that supports an isolated population of a species that used to be common, but is now only found in this specific area. So yes, just as the word suggests, a refugium is a refuge! When it comes to your home aquarium, though, you won’t have to worry about maintaining an endangered species. 😉
We love adding refugia to our tanks because they’re the perfect place to do, or keep, anything you can think of that isn’t ideal to do or keep in the main tank. Do you have fish that eat copepods or macroalgae? Breed those in the ‘fuge. Need a place to grow out frags? ‘Fuge. Got a fish that’s bullying its neighbors and needs time-out? You guessed it… ‘fuge!
The advantages of the refugium don’t end there. Most of us know by now that a larger water volume makes for a more stable aquarium, so the extra water (and surface area for beneficial bacteria) introduced into the system along with your ‘fuge are very helpful. If you grow phosphate-munching macroalgae in there, you may even get away with fewer water changes.
And the best thing? Setting up one of these refuges is a breeze. Technically, your refugium could be as simple as a food-safe storage tub with an old pump and some hoses.
What do you need to set up a refugium?
Not that much. If your aquarium already has a sump — an extra tank, consisting of multiple compartments that hold equipment and additional biological filter material — it’s as simple as expanding that or even just moving some stuff around to make room. The aquarium water is already being circulated through the sump, so no need to install a new intake and outlet.
No sump? No problem. You can go the ambitious route and install a full sump with a refugium section, or just keep it simple by popping a simple “Mini-Me” under the main tank and routing the water through that. Add a layer of substrate to help buffer the KH and offer beneficial bacteria a comfortable home. The flow level can range from trickle to Niagara Falls, though don’t let the water go stagnant.
If you’re not sure how to go about routing your aquarium water through an additional small tank the DIY way, your local aquarium store should have full sets available that come with all the necessary components. Or contact FantaSEA Aquariums to build your refugium for you!
Hang-On-Back Refugium
No sump and no space? You can still have a refugium! If you’ve ever had a close look at a hang-on-back filter, you’ll have noticed it’s actually a lot like a hanging mini sump: located outside the tank and filled with filter material. All we have to change to turn a HOB into a refugium is to make it bigger and replace (some of) the bioballs with living macroalgae.
Although its footprint is pretty small, a hang-on-back refugium is still plenty to grow macroalgae, plus house some critters if need be. The water is pumped past the algae so they can work their cleaning magic, then returned to the main tank.
What to put in your refugium
Macro-Algae
The main reason most aquarists install a refugium is to harness the incredible nutrient absorption power of macroalgae, particularly Chaetomorpha. Chaeto is a huge guzzler of phosphates, nitrates, and other micronutrients that can cause algae growth when left to accumulate.
The nice thing about Chaeto is that it doesn’t “go sexual”: unlike many other macroalgae, like the decorative Caulerpa, it won’t try to reproduce by releasing clouds of gametes into the water. That’s a good thing, because when a macroalga does this, it pumps a lot of the nutrients it previously absorbed back into the water.
If you’re looking to use macros like Chaetomorpha in your refugium (and we certainly recommend you do), remember they do need light to photosynthesize. Special lamps for macroalgae exist — you’ll recognize them by the reddish color of their light, as opposed to the blue/purple spectrum we use for our corals.
Tip: Herbivorous fish species, like the popular yellow tang and rabbitfish, love nothing more than munching macros. This means you can basically grow your own free fish food in your refugium.
Copepods
Copepods come in all shapes and sizes: Mother Nature went ahead and made a whopping ~13,000 different species. Some are nightmare fuel, like the parasites known as fish lice, while others live in freshwater. However, there are some saltwater copepod varieties you’ll definitely want in your refugium!
All aquarists love pods. They aren’t just cute to look at, like tiny, clumsy shrimp, but also act as an in-house cleaning crew. Some fish eat them; in fact, the popular mandarin goby refuses to take anything else, which often results in starvation in captivity. If you want to boost your copepod population or grow free fish food, releasing a swarm of these little crustaceans into your refugium is an excellent idea.
Already got copepods in the display tank? You can move some of those into the ‘fuge. If you don’t, just buy a starter population online. Try Tisbe pods for something small, or Tigriopus for a bigger variety. The popular Apocyclops doesn’t reproduce much in full salinity and is thus best used in brackish tanks or as a one-time fish snack.
Once the copepods are in your refugium, you don’t really need to do anything. They don’t even need a light and will feed on phytoplankton and detritus, multiplying as they go.
Frags & corals
Corals growing like weeds? Frag them and move them to the ‘fuge to heal. Depending on the size of the refugium you’re using, you could house an entire coral fragging factory in there — free from the bothers of nippy fish and clumsy invertebrates.
You can even use corals in your refugium as a handy addition to the nutrient export army. Macroalgae aren’t the only thing that absorbs phosphates and nitrates! Vigorous coral species, like pulsing Xenia, also work well. Throwing a stalk in your ‘fuge and watching it grow there is a good way to enjoy this pretty number without the threat of it overtaking your display.
Time-out & separation
Got a rogue crab that you’d like to keep, but that is eating your corals? Or maybe a bullying fish you want to give the rest of the tank some relief from? A new addition you need to ensure is eating properly before introducing it into the main aquarium? The solution in all these cases is a refugium.
Some aquarists even use their refugiums to house extra-deadly creatures that would wreak havoc in their display tanks. If you’ve got the space, a ‘fuge can be a great place to keep something like a mantis shrimp without running the risk of your other livestock getting clobbered.
Conclusion
There are endless reasons to connect your aquarium to a refugium, and very few reasons not to. Even money doesn’t have to be a concern: a sturdy, food-safe storage tub with an old pump and some hoses will do the trick. In return, you get polished water and better overall aquarium health. What more could we ask for?
If you’re thinking of setting up a saltwater (or even a freshwater!) aquarium with a refugium but aren’t sure where to start, the FantaSEA Aquariums team can help. We can design, build, and even maintain your dream tank for you, so all you have to do is enjoy it.
