It just isn’t enough to say that a refugium is “a tank on a tank” or “a sump with some macroalgae in it.” When used to their full potential, refugia make for a far more dynamic—yet more stable—captive ecosystem. Though they are typically smaller in size than the main tank, refugia play a major role in supporting the very base of an aquarium system’s food pyramid. Traditionally, they are used primarily as nurseries for Nature’s basic foodstuffs, namely algae and pods.
It’s pretty hard to overemphasize how important the concept of the refugium has been to marine aquarium keeping (and it is, at its heart, a concept rather than a mere piece of equipment). Many aquarists joke about how they set up their first refugium—technically as a “filter,” after their significant other demanded that they acquire no more “fish tanks.” Even so, after running a refugium for some time (and seeing the marked improvement in the health of our animals) many of us would never even consider building another system without one. Nowadays we keep a great variety of plants and animals in them, sometimes even blurring the line between display and purely utilitarian purpose. But let us not forget their nominal function!
[Refugium]
In the Beginning There was Light, Algae and Pods
If there was a single element of system design that radically changed the way we keep marine aquaria (and certainly our odds of keeping them successfully), it was the sump. Perhaps this came about from the need to drop water to lower levels for “trickle” filters, which really began to become commonplace by the mid-1980’s. But aside from the advantages of so-called wet/dry filtration, we saw so many other boons to this technique. For example, by drawing water from the surface, much floating waste such as oils and foams could be more easily removed. Most significantly, we could move much equipment away from the main tank (where it was an unwelcome distraction from the display).
As we figured out ways to centralize this clutter in our sumps, they evolved into a sort of little hidden workshop. In a
sense, these consolidated clusters of gadgets became the brains of our system—the core of the filtration system, if you will. However, we did not even consider using these “extra” tanks to house living things (aside from bacteria). This all changed fairly quickly (and just as sump-based systems were becoming the norm) after reef aquarists started to hear about the work of one particularly industrious marine biologist at the Smithsonian Institution.
Dr. Walter Adey was already using the term refugium to refer to any space in an aquarium where certain organisms, specifically those at or near the bottom of the food chain, could subsist without being consumed by other aquarium inhabitants. Originally, this could have referred to any safe haven including deep pockets in the rock structure. But Dr. Adey went one, or two, steps further.
This was an especially difficult time for marine aquarists, many of whom wanted to be reef aquarists. The major impediment to keeping (particularly stony) corals at that time was overgrowth by nuisance algae. In light of the costly failures it caused, to call benthic microalgae a “nuisance” seemed a huge understatement. In due course, we tried all sorts of things to control algal plagues. This included (1) the addition of herbivorous “pods” such as copepods and amphipods as well as (2) nutrient control via the addition of macroalgae and/or deep, denitrifying sand beds. Acting on a stroke of genius, Dr. Adey put all of these things together in a single, separate but connected tank.
The experiment was wildly successful. Kept away from large herbivores such as tangs and maintained under a concentrated light source, the macroalgae thrived. The connected tank itself worked well as a settling basin, collecting detritus that provided additional nourishment for the microcrustaceans within. As their populations exploded, these protected pods steadily spilled into the main tank where they were readily consumed by small fishes and corals. This extremely effective system was immediately duplicated and improved upon by many others. The word refugium was forever after meant specifically as a pod refuge of this specific kind.
The Ideal Refugium
Over the course of the last few decades, the concept of the refugium hasn’t really changed very much. Let’s just say that it didn’t need to change; as it (1) focused on producing a good supply of a natural food source and (2) served well to protect algae and pods while providing them with an ideal living space, it didn’t require much improvement. That’s not to say that improvements haven’t been made to refugium materials/design.
Today, for example, we have much better aquarium lighting technology. Some types are even specially designed to

grow macroalgae and are thus very well suited for use on refugia. Refugium tanks are themselves better than ever. Deluxe models such as the AlgaeBarn Triton Style Sumps by Crystal Reef Aquatics offer highly specialized spaces and fittings for certain pieces of equipment even while providing a large, dedicated compartment for use as a refugium. Additionally, there has never been a better selection of both pods and macroalgae. Best of all, the availability of quality live phytoplankton and bacterioplankton such as OceanMagik and PNS Probio™ respectively have made it even easier to maintain sizeable pod populations.
So what does the future hold for the refugium? That is pretty hard to say for sure. Like so many things in the marine aquarium hobby, just when we think we’ve finally mastered something, along comes another big innovation. And it’s really the pursuit of new innovations that keeps the hobby interesting, is it not? Algae and pods will of course always be at the center of refugium keeping. Still, aquarists will perhaps work with many more species of macroalgae, copepods, phytoplankton, etc. in coming days. It is certainly possible that even more refinements of refugium design are to come. There may even be other, novel methods of refugium keeping to try out. But one thing is pretty certain at this point: refugia really, really work and they are here to stay!
[Refugium]
polygonreef says
Sweet one! Love the auricle!
Michael Gary says
Great article
Jason W Beguhn says
I seeded my second tank with your 5280.
Jason W Beguhn says
I seeded my second tank with your 5280. Every two months I add a bottle of 5280 pods.
Jordan pitts says
I find my tank looks a lot better when my fuge is stocked with pods from algaebarn
Michael says
These are so overlooked, I’m surprised more people don’t set up effective ‘fuges in their systems.
Compy Ginorio says
A fuge without pod’s is like a garden without Rose’s. A well stabilized refugium is a great and effective tool in your tank balance.
Compy Ginorio says
A fuge without pods is like a garden without Rose’s. Refugium is a very important part of my system.
Compy Ginorio says
A fuge well establish makes a great difference in the overall Tank health.
Jeremy says
Love the advice
Jose says
Thanks for the info
Eduardo Govea says
Refugium is definitely a great addition to a reef tank. The Algeabarn refugium kits is amazing and close.
robert vice says
my ulva I’d full of them
Taylor hahn says
Refugiums are very versatile for our tanks!
Cole B Presley says
I need to make a real fuge in my new tank once I get it
Beth Villmow says
Certainly makes”natural” reef-keeping much easier and healthier for the creatures in your aquarium!
John key says
Now I know what I’m going to do with that spare tank I have sitting around 🙂
Steven Lombardi says
I don’t think I will have another tank without a fuge. So helpful for so many things.
artaa1988 says
cant wait to build a fuge for the my bigger salt tank i have in storage waiting to come to life
Jose Pacheco says
Now I’m thinking to star small tank just for mangrove and pods
Robert says
Love this article please keep them coming
Martin Oldham says
this is unreal amazing
RICHARD W SMITH JR says
The macro order I recieved from you was beyond expectations. Thanks again, and by the way, my girl is growing flowers from seed in the plastic Mason jars 😉
Gabriel L Nguyen says
Great info since I’m trying to set up a refugium for my reef tank!
CHRISTOPHER SHELTON THOMAS says
after trying many other methods a sump with refugium has provided the best long term results.
Steve says
Is there such a thing as having too small of a tank for a refugium? Or Is it even more important?
Ryan mcmillon says
Thata exactly what I said no more tanks …..we go a new sump last week
giddetm says
great story
snowseifert says
Love this story
Evan says
Wow, great information
Matt Moline says
I have a HOB refugium. I have chaeto and pods
david says
I will soon be setting up a refugium, and I’m looking forward to the benefits my reef will get.
angelyrojas23 says
Great info
Drew says
Awesome!
Jeff B says
Ive got room for a fuge in my sump, need to get it set up!
Rich Knox says
I’m ready to start my refugium!!
Jered Hedrick says
Hoping my Kessel will work wonders with our chato that is coming soon.
Yakov Elizarov says
Their macro algae is by far cleanest and best in market. Product packaging superb
Tyler.gore.90 says
My entire new build is planned around how my refugium will benefit my tank. Which at first was working too well.
Adam says
Love a big ol’ refugium!!
motor795 says
I’m ready, just need to not have a sumpless tank
sdemarco62 says
Really thinking of moving my refugium to a seperate small tank and plumbing it into my sump.
Cole Goracke says
Those are sweet sumps!
Matt yeager says
Awesome info. Looking to starting my refugium
ReeferReefer says
I would like to see a study on using mangroves for nutrient export. Are they actually effective?
Finn says
My display tank IS my refugium.
Justin says
Looking forward to getting mine set up.
David Hillen says
great article
Chas Johnson says
I want a prize
WILLIAM WAHL says
Great article! I have a refugium on every tank I setup!
chris.singelman says
Great article! I learned a lot?
zadok jollie says
After reading this I’m defiantly setting up a refugium on my next tank.
Shawn Benton says
Gonna work on one of these!
Sean Simkins says
I need a better fuge so bad
Doug putt says
always have a refugium!
Michael Wahl says
Great article about algae.
danieoue says
useful information. Thanks!
Cathy robbins says
Do you even have a reef if you don’t have a fuge lol
Scott Chase says
I run a refugium on all my tanks
JW says
The only thing is I don’t use a sump! Not sure I want to set one up just to grow copepods unless maybe I set up a separate tank.
eric m sear says
love it
Darell says
Excellent info
james says
Want to try a BIG Mangrove sump when i put up my new tank
Allen says
A refugium is a must, where else are all those pods gonna hang out
Tara Fuller says
Could be good for a extra tank. Great info thanks
allison Dale lisney says
On my next tank, there will definitely be a fuge!
Josh Veloe says
Going to have to do this with my 10 gallon tank
mamucher says
Great information
Ak Reefer says
The more pods the better!
Kelly Tompkins says
I don’t have substrate in my refugium. After reading this article I might have to rethink my stup!
Joshua Andersen says
I like to keep it ol’ natural with a refugium
Stacey says
I added your post to my fuge, and the overflow into my DT supports a pair of happy fat mandarins with plenty left for the other inhabitants of my tank ?
CANDICE FONG says
great and helpful article!
Brett says
A refugium is almost a must for a reef anymore. They really do help so much.
Matthew Lucero says
great work
Tim J says
Refugiums are such a great way to keep a food web in a reef tank and help manage nutrients.
Bobby Daniels says
Love this article please keep them coming
CHRIS MATHIS says
Fuges are great for filtration and fun to watch them explode with life.
Ben presley says
Great info. Thanks
Tami says
This is why I got a new system and am getting a sump.
Alex Lin says
my refugium is a pod heaven!!
lawrence zapata says
Im about to upgrade to a bigger tank with a sump. So refugium it is.
hathcock.sam says
Great reads and info for anyone in this hobby….Been in saltwater aquariums off/on since the 70’s in college….getting back in it knee deep….My oh My How things have changed….Technology…But the “Same”…..Waiting on my first order from AlgaeBarn – copepods5280 / Ocean Magik / Tigpods / Chaeto – RedOgo – Sea Lettuce….already have live sand and rock in place in my first Refugium…..and Its gonna be fun again
Sam
Eugene Botts says
I run a 36″ PM pro full of Chaeto, sand and live rock with a couple mangroves. Definitely keeps the pods healthy and keeps my nutrients low without a skimmer.
Justin says
Thank you!
Tony Holliday says
A good display refugium is one of my dream plans.
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