I am starting up a saltwater aquarium once again. It is going to be a reef tank. The aquarium I have now is only a 20 gallons so I was thinking I’d convert it into a refugium and buy a larger tank for fish and plant life. What is the largest aquarium a 20 gallon refugium can feed?
A refugium, as defined in the aquarium hobby, is as an area or refuge where micro-organisms can live and breed without the worry of predation from fish or other organisms. Macro-algaes are also kept in refugiums to aid in waste (nitrate and phosphate) removal from the aquarium’s water. Many people setup refugiums as part of the filtration system for their saltwater aquarium, especially with reef tanks, where nutrient control is a huge concern.
So what size refugium should you put on your tank?
While there are many different opinions on this, I feel most people will agree a refugium should be at least 10 to 15% of the tank’s volume. So for a 55 gallon tank, for example, a refugium should be at least 5.5 to 8 gallons for it to function properly for that size tank.
But what if you don’t have the space available for something that size? Will a smaller refugium work? “Kind of” is the best answer I can respond with for that question. In my humble opinion, something is better than nothing, but you certainly can’t expect a smaller refugium to perform as well as a larger one.
You will need to provide adequate lighting in the proper spectrum to keep macro-algae alive. You can use fluorescent lighting, such as normal output bulbs, power compact, T5 and VHO bulbs or plant grow spot light bulbs. If you really want to light things up, you can even use metal halide lighting. But remember: you don’t need to make the tank look pretty, so stay away from higher Kelvin-rated bulbs. Normally bulbs under 6700K work best to achieve good growth from your algae.
Does flow rate matter through a refugium?
This again is a topic that has a lot of differences in opinions. I personally have setup refugiums with high flow rates and ones with minimal flow rates and, in my opinion, they both work … provided you don’t have a movement so slow things become stagnant in the refugium or movement so fast it literally blows the algae or sand out of the water. Generally speaking, a nice, moderate flow through the refugium will work just fine.
Macro-algae should be at the top of your list. There are many different types of algae available that will work well, but most people are leaning toward using Chaetomorpha (or spaghetti algae) over Caulerpa species. The reason for this is two-fold. First, Chaeto (as it is oft-times shortened to) is fairly hardy and grows fast. It grows into a fairly dense formation that is a perfect refuge for micro-organisms like copepods, amphipods and such. The second reason is Chaeto tends to be a “non-invasive” species and can easily be removed for pruning. Caulerpa attaches itself to anything porous and, once established, can be very difficult to remove from the refugium. Also, while I have never actually witnessed this, people claim Caulerpa can go “sexual.” Basically the Caulerpa releases all of its chlorophyll and causes your water to turn green.
Live rock can also be placed in your refugium. The live rock will not only help seed the refugium with micro and macro organisms, it will also give them places to hide as well. A few smaller pieces of what many times is referred to as “live rock rubble” can help kick start a refugium.
Mangroves are another neat item that can be used in a refugium provided you allow space for its upward growth. Most of the mangrove will actually be out of the water with only its root system fully submerged. While they are not the best at taking up nutrients from the water, they are very neat to watch grow.
Fish is at the top of that list. If you put a fish into your refugium it can, in a matter of days, wipe out the copepods and amphipods you are trying to grow. Do not put fish in there. Certain crabs, such as Arrow Crabs, are well-known for their ability to feed upon bristleworms, so many crabs should be excluded from being allowed in. Sand sifting starfish are another one to mention since these guys can decimate the life of a sand bed very quickly.
Can you make a display refugium, or does it have to be hidden?
You certainly can make your refugium on display for everyone to see, but if you are like me, you will want it to look as good as your main tank. This will create more work for you, but as long as you don’t mind that it can certainly add another topic of conversation when people are viewing your tank.
Overall there are really are no drawbacks to adding a refugium to your tank, whether it is a fish-only (FO) or a reef system, except for maybe the time and cost of setting one up (if you consider that a drawback). They can be very beneficial to the overall health of your tank by not only adding a food source for your fish and corals, but also by providing a very natural filtration to your tank. I have listed a few links with discussions along with a few recommended books if you want to find out more about refugiums and the benefits they can provide for your aquarium.
Macro-algae and refugium discussions
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