Refugium Basics

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  1. jhnrb

    jhnrb Moderator

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    REFUGIUMS, AKA. FUGES, OR, REFUGE

    What are the basics of a refugium?

    A REFUGIUM is a living filter. The intent of a refugium is to dedicate a specific space for the growth and/or cultivation of algae or animals where they can be protected from predation. A very basic refuge would be a hang on back filter. When changing the filter pads, look closely and you will see all kinds of worms, copepods/amphipods. These pods have found that they can live free of fear in the filter pad because fish can not get to them. Thus the basic refuge is born out of a simple hang on back filter and filter floss.

    What are the benefits of a refugium?

    A refugium is basically a container that has been set as a place to grow macro algae to feed hungry tangs or as a form of natural filtration. Fuges can also be set up as a place to grow amphipods/copepods (pods). Depending upon your needs, you can even use a refuge as a place to keep other creatures that you can?t keep in your main tank.

    Refugiums can act as living filters to restrict growth of undesirable algae by utilizing the concept of nutrient export with other more desirable macro algae colonies living within the fuge. They also act as a farm to cultivate and grow pods so as to act like a natural food source for fish and invertebrates. A properly sized refuge can also help balance your tanks PH chemistry via macro algae on a reverse photoperiod. Just like the addition of a sump, the refuge can also add to the total water capacity of the system, making it inherently more stable.

    What size should I make my refugium?

    Your refugium can be any size you want, but its suggested by Fenner and Calfo (Natural Marine Aquarium Volume I ( Reef Invertebrates) that the larger the refugium the more of a benefit one will see from it. A suggestion of 20% of the size of the display tank is given as a way to size a large and productive refugium. A refugium that has a total capacity of 10 gal will be much better suited to a 55 gal display tank than a 5 gal refugium or a refugium of even smaller size. This is simply because of the volume that the refuge can hold. The bigger the fuge the more algae it can hold or the more substrate area you will have to cultivate pods. Having a refuge that is too small can be just as limiting as not having one at all.

    What can I put in a refugium?

    The most popular use for a refugium is to grow macro algae for nutrient export, PH stabilization, and as a food source for hungry tangs and angels. This is by no means the only use for a refugium. Refuges can also be set up to cultivate plankton or amphipods/copepods. Refuges can also be set up with DSB's(Deep Sand Beds) and be the sole source for nitrate export. Let us say you have an established aquarium with a crushed coral substrate and you don't want to go thru the effort of removing the old substrate and putting a in new substrate. Adding a somewhat large DSB refuge will provide for a means of nitrate export. To have a viable DSB refugium its suggested sizing your refugium at no smaller than 20% of your tank volume but ideally the larger the better, the depth for a DSB refugium should also be between 4-6"(the depth is a debatable subjec depending on who you talk to. a subject for a future article).

    If you're using the refuge as a nutrient export device, then you will need to light the refuge just like you would your display tank. The macro algaes you want to grow need proper lighting for photosynthesis. Ideally you should light your refuge on a reverse day/night cycle from your main tank. What this means is that while your tank is lit the refuge is dark and when your tank is dark your refuge is lit. The purpose of this is to provide a continual CO2/O2 exchange, thus maintaining a consistent PH level within the tank. (Some hobbist run their refuge lights 24/7.)

    If you want to provide a place for pods to thrive then you need to provide an ideal living environment. This would first be a place with no natural predators. Second you should have either a thin later of sand or bare bottom and provide a nice mound/layer of rubble rock. Amphipods and copepods will find this kind of habitat desirable. The pods should then find their way back into the tank when they are moving about at night. A pod tank does not even need to be lit.

    As you can see the exact setup of your refuge will really depend on what you want to keep in it. Think about what kind of task you want your refugium to perform and then design and size it appropriately.

    How do I incorporate a refugium into my setup?

    There are two main locations hobbyists put their refugiums. You can either position it above the tank or below the tank. Some hobbyists will put their fuges above the tank so as to, keep from chopping up pods, when they enter the return pump. I don't believe in this because at some point the pods will have to travel thru a pump either to get into the refuge or to get out of it. Remember my example above about a simple hang on back filter being a very basic refuge. Well no one put those pods in that filter where they found the filter floss to be their home. So that means they had to have traveled up the intake tube and thru the intake impeller to find them a home in the filter floss.

    If you put your refuge above the tank then you will need to plumb it in such a manner that you have a pump either coming from your sump or from your main tank to feed the refuge and then set up a gravity drain to return water to the main tank. Never try to set up a dual pump system where you have a pump putting water into and a pump taking water out of a system. The problem with such a setup is that it will be next to impossible to maintain a duel pump system operating where both pumps are moving the same volume of water over a long period of time.

    Putting your refuge below the tank would entail a setup just the opposite where as you have either a gravity feed from the display tank into the refuge and then a pump returning to the main tank or you could have the refuge on a secondary circulation set up feeding out of the sump and back into the sump or back into the display aquarium. ( remember which ever system you attempt make sure you do not set up a situation that could lead to overflow of either the sump, the main tank, or, the refuge.)

    How much flow should I run thru my refugium?

    The flow rate that will optimize your refugium will greatly depend on how you have your refuge set up. If you're using it for nutrient export then shoot for a turnover rate of five times your tank volume per hour. If you're using your refuge as a pod farm then you can increase this flow rate to ten times your tank capacity if you want. If you're using the refuge as a plankton farm then you will probably want a flow rate much lower than even five times the turnover rate. (flow rates are a matter of who you talk to. will be a subject of a future article).

    In summary, remember that you're not limited to what you can do with your refugum and that you can even install multiple refugiums on the same system. The size of the refuge should be as large as you have capacity for and while the flow rate does not have to be equal to the flow rate within your tank, it also does not have to be so low that it could be classified as a stagnant body of water.

    References:
    -Natural Marine Aquarium Volume 1 ? Reef Invertebrates by Robert Fenner and Anthony Calfo
    jhnrb, Oct 14, 2005
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    benry likes this.
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  2. jhnrb

    jhnrb Moderator

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    Refugium (primer)

    MORE ON REGUGIUMS

    The addition of a refugium, or sanctuary / isolated area, incorporated into a marine aquarium offers several beneficial effects. I think that enough messages on numerous mailing lists on the Internet have made that clear. The eggs/larvae and other nutrients that migrate from the refugium to the tank represent food for the corals and the fish in the tank.

    1) Live Food Production Area: The refugia chamber is usually designed to be separate from the main aquarium (or esthetically built into the design of the aquarium as in the ecoReef ™ system) yet included within the water column. In most cases the refugium is built into the sump attached to an aquarium. It can be a square, rectangular, round or what ever shape you desire. The shape is not important at all. You can make it any shape you wish that fits your sump or your needs best. I have even seen one in an unused corner overflow box that had been modified to act as a refugium at an aquarist's home in Atlanta.

    In many cases though it is a small separate area in the sump that supports filtration, and water recirculation for your tank. The area will vary in size depending on how large your tank really is. I have seen refugia as small as 6 inches by 6 inches by less than 1 foot tall on a 75 gallon aquarium, and I have seen refugia as large as a total of over 600 gallons of water, associated with multiple 1000 gallon vats at AWC in Cleveland TN. Size is not all that critical but, of course, the smaller the refugium the less animal life you will be able to place in it. The less animal life in the refugium, the less food stuff that will migrate to your aquarium.

    Small food organisms and animals can reproduce in the absence of predation. In fact that is what refugia are all about. Pairs of micro-crustaceans (i.e. glass, mysid, and peppermint Lysmata sp. shrimp, etc.) that reproduce on a regular basis can be kept in the refugia allowing their larvae to flow into the main aquarium. This routine influx of micro funa becomes food for fish and invertebrates. This is the main advantage of refugia. Food flows on a near constant timeframe from the refugium to the aquarium where corals and fishes can consume it. This is a major advantage as you are supplying your animals with a constant supply of live foods vs artificial ones.

    2) Settling area: Low water flow through the refugia allows suspended solids (i.e. uneaten foods, fish fecal matter, etc.) to settle out in this area. This detritus can periodically be removed by siphoning it out, or it becomes food for detritus eating animals housed within the refugium.

    By low flow we mean 1 x the content of refugium per hour. To give you an example: if the refugium contains 3 gallons, you would flow 3 gallons per hour through it. That seems low. Yes it is but it is enough. You can go up somewhat higher, say 2 x per hour, but that is about as high as I would recommend. Too much flow created too much water movement and that would force some of the fragile and small inhabitants of the refugium to be pressed against the sides of the refugium where the water exits it. This will become clearer later.

    3) Nutrient uptake: The refugia can also serve as an asylum for macro-algae for those Aquarists that for one reason or another do not, or can not, keep plants in the main display aquarium. Ammonia, nitrate, phosphate, and heavy metals are food for plants and in most cases pollution or toxic to animals.

    Refugia with macro-algae or with mangroves tend to be larger than refugia without them. This is necessary to account for the space needed for the plants and especially for the mangroves if that is what you use (and such is an excellent idea by the way). Mangroves make excellent nutrient sinks and uptake mechanisms for all tanks and do well in any kind of refugium, especially when planted in mangrove mud.

    These unwanted elements that can be toxic are "locked-up" (consumed) in the algae or mangroves during their growth. Photosynthesis or the process by which plants use light as an energy source to synthesize carbohydrates from CO2 and give off oxygen is also very beneficial, as it will increase the overall amount of dissolved oxygen in the system (aquarium) for the benefit of all animals.

    If the refugium area contains plants and is lit on a photo cycle opposite the main tank (Reverse Daylight Photosynthesis RDP ™ ) it will help to maintain a more stable pH by removing the CO2 produced in the main tank during the nocturnal photo period. RDP will also help maintain a saturated Dissolved Oxygen (D.O.) level during the period when all the oxygen producing plants and animals become producers. This i not necessary but is beneficial and has been proven to be so by several advanced experimenters. You can, however, run the lighting over the refugium on the same cycle as the main lighting of the tank.

    RDP eliminates a good deal of the pH fluctuations that occurr during night and day. Some claim that this is beneficial and reduces stress and others feel that in a well balanced aquarium this is not necessary. Our suggestion is that you try it both ways and decide what works best for your aquarium. Run the lights over the refugium (if it contains macro-algae or mangroves) on the same photoperiod as your tank for some time and keep track of what goes on. Make some photos perhaps so you have a record to go by.

    Then, after you have done so for a few weeks (we suggest about 10-12) then switch to RDP and run that for a number of weeks, and again keep track of what goes on. Photos help a great deal of course, as they will allow you to compare how the tank looks under either format a lot easier. You need not make high quality super shots, just good photos that clearly show what the animals look like under both conditions.

    It also helps to have the photos evaluated by a third party. This brings more objectivity to the process. Let someone you know tell you what is best. Since they do not know what kind of lighting you were using, you will get some excellent feedback, allowing you to decide what is best for your tank. Note that RDP will not be the preferred method for "all" tanks but it may be for yours. Find out ...

    At The Aquatic WildLife Company (note that this is true in general and for every kind of refugium) we have found the following items work well for establishing a refugia: (this is a suggested combination "Package" of items that would be placed in a 10 gallon capacity refugium connected to a 50 to 100 gallon aquarium)


    a) 2 pounds of live sand
    b) 25 gammarus shrimp
    c) 2 small mussel rocks
    d) a bag of assorted plants or several mangroves
    e) 10 Stomatella varia snails
    f) 5 blue leg hermit crabs
    g) 4 turbo type snails
    h) 1 small brittle starfish
    i) 1 small common cucumber.
    You should be able to get all of the above for less than $100.00

    Note, again, that the turnover rate is 1 x the content of the refugium/hour and that you can go a little higher but not much. The way a refugium is set up must let water in and out of that area and often this occurs through a screen type panel on one side of the refugium area.

    This screen lets some of the animalcules through (so they are uptaken by the corals and fed on by fish) but keeps the majority of the animals inside the refugium. When the current gets too strong, some of the small inhabitants will be forced against the screen and will not be able to swim or move away from it and will end up dying. The reason for keeping the flow low is therefore simple: the survival of what is in the refugium.

    The mesh size of the screen determines how large the lifeforms are that can get through. 250 microns is just fine and will let enough food particles through for nutrient uptake by corals and other filter feeders in the tank. If you find that too much or too little passes through the screen, you can always change it at a later date.

    Where do these come from? They are the result of reproduction inside the refugium. That is the whole idea. You keep the brood stock in the refugium and you let some of the eggs, larvae etc. get out through the screening.

    Remember to clean the screen from time to time as dirt will settle on it and will block the flow of water and food stuff.

    END.
    Last edited: Oct 8, 2006
    jhnrb, Oct 8, 2006
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    Adam Picard, benry, Nevek and 4 others like this.
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