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What Is a Marine Aquarium Refugium?
Several years ago, FAMA and other aquarium periodicals brought the refugium to our attention. It resulted in a flurry of "how-to's" and "why for's" that occupied many pages in many magazines and continues to be the subject of new inquiries. So, from a non-scientific and hobbyist's perspective, let's talk refugium!
Essentially, a refugium is nothing more than a refuge from predation. Sessile inverts 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 (see diagram above), the refugium allows for common water filtration while at the same time keeping more aggressive fish from impacting it.
What follows is a diagram showing a simplified refugium setup. Notice how the water is delivered to the unit and how it drains back into the display tank and/or sump. I'll take this opportunity to point out that a true refugium is NOT a reverse photosynthesis device—those are another animal altogether! The true refugium is meant to be SEEN, as is the main show tank. Reverse photosynthesis arrangements are meant to be installed in a sump beneath the display tank and are a means of primary biological filtration. This is not so of the refugium.
The focus here is to provide a "quiet" zone for Seahorses, Peppermint Shrimps, Copepods & Amphipods and other denizens that would otherwise not last long at all in a community tank. While benefiting from the improved water quality that most reef systems provide, this isolation allows for spawning in our shrimps or other animals, as well as providing a nice sand bed for beneficial worms and other sifters.
When contemplating installation of a refugium, several factors should be considered. First, where are you going to set it up, or place it? Most agree that placing the refugium as close to the main tank as possible is the way to go. Many aquarists have simply set a 10-gallon aquarium on a table next to its big brother. This works but requires a water return pump unless draining back into a sump or main tank. So where does the water supply come from, and where does it go?
Next Page > Plumbing the RefugiumContinue to 2 of 3 below.
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Plumbing the Refugium
Time to make a point: The water entering the refugium should come from below the main tank's water surface—not from the overflow—if so equipped. Why? Surface water is skimmed from the main tank into the overflow. This surface water is laden with oils and other dissolved organics. Why would you want to dump this into your refugium? Better to place a small powerhead inside and just below the water surface of the display tank to provide oxygenated H²O. Better yet is to tap off the return line... from your protein skimmer. Highly stripped and highly oxygenated water from the skimmer provides as near ideal water as we can expect.
Draining the refugium back to the sump allows gravity to do the labor for us. If your system is sump-free, then mounting your refugium above the main tank waterline or behind the tank may be desirable.
Ok, we have established what a refugium is and how it should be connected to the balance of your existing system. We have seen why it's important to consider the right plumbing and to plan accordingly. Now let's discuss what to place inside, preparatory to introducing our animal load.
Next Page > What To Place Inside the RefugiumContinue to 3 of 3 below.
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What To Place Inside the Refugium
We have established what a refugium is and how it should be connected to the balance of your existing system. We have seen why it's important to consider the right plumbing and to plan accordingly. Now let's discuss what to place inside, preparatory to introducing our animal load.
Live sand and rock: I favor live sand and some live rock work. Since primary filtration is not an issue, the aesthetics of your creation take priority. I would recommend a sand bed at least 1-1/2 inches deep, 2... inches being better. Ten gallon aquariums aren't all that deep, so you will have to judge the sand thing for yourself. My idea when erecting my first refugium was to establish an area for natural denitrification. This aids both tanks being linked to a common water source and a deeper sand bed makes this possible. I used live aragonite sand, however, there are many sources for sand, as well as live rock. The few pieces of rock rubble that I used came from my main tank—plenty to go around. Once again, if using the main tank's filtration, biological considerations are not necessary.
What about lighting? I have seen a few ideas that allow light to be redirected over the refugium, but they were stop-gap measures. Better to have a proprietary lighting system designed strictly for the refugium. A 6500K and a mono-phosphor 7100K blue provide nice lighting for a tank this size. I recommend Energy Savers Unlimited (ESU) Coralife bulbs, or similar OSRAM lighting. These are ideal units that feature twin OSRAM fluorescent bulbs in a neat aluminum reflector. By swallowing the water column via the sand bed, these OSRAM will give the intensity needed for your refugium inhabitants. Being just 9 watts each, they radiate at a 75 watt, incandescent level. That's equal to 150 watts of incandescent light in a 10-gallon tank! That's plenty of beneficial illumination. I used egg crate cut to the inside dimensions of the tank frame and simply placed the reflector on this to create an instant light hood. The reflector keeps stray light out of your eyes and keeps the rest of the room comfortable.
In conclusion, all we are striving for here is to provide a safe and quiet haven for our animals to flourish. I allowed callers to grow, and even cultured some Halimeda algae as well! I placed two Garden Eels in my original setup. Did you know they were excellent jumpers?