A [tag-tec]refugium[/tag-tec] (or a fuge as they are commonly known) is a small aquarium which either sits next to, hangs upon, is below the aquarium or is above the existing aquarium. A refugium is normally a mixture of a deep sand bed or a mud bed combined with macro algae, however a refugium can also easily be made using a shallow sand bed and macro algae. If a substrate is provided that the macro algae can grow in then a refugium can be made.
A refugium is similar to that of the sea grass beds which are used in nature albeit on a smaller scale.
In an [tag-tec]aquarium refugium[/tag-tec] any detritus which enters the aquarium will settle down onto the sand/mud bed and be processed. In the substrate various organisms will live, reproduce and consume – as with a deep sand bed, plenum etc you will need to introduce these creatures into this area, this can be from some pieces of live rock, some sand from another sand bed or from some grunge from your local fish shops curing vats.
With there being no fish in the refugium there is no predation (except perhaps among the micro organisms), therefore all of these organisms have the ability to reproduce and multiply, enabling you the aquarist to have a natural food source for your aquarium. Macro algae is grown in the refugium and extracts nutrients from the water passing through it. The addition of the macro algae reduces nitrates and phosphates for example and enables a low level of these nutrients.
Normally lighting is applied to the refugium on an opposite cycle to the display aquarium lighting. This is also beneficial as oxygen is provided during the night time hours therefore stabilising any pH fluctuations which can otherwise occur. As with other algae based systems it is better to light the aquarium with lighting which is designed to maintain and support plant life. Lighting which is in the range of 6000 kelvin will be more than sufficient as lighting at this level produces a lot of red and yellow which plant life like.
A refugium is quite simple to add to the aquarium system. It can either be installed directly in the sump if a partition is provided or next to/above the main display aquarium. The benefit of housing the refugium next to or above the display aquarium is that some of the various organisms which live within the refugium will overflow with the water back to the main display aquarium. Sometimes this is not always possible though and a lot of aquarists build a refugium in or next to the sump. The only disadvantage of this is that any organisms which overflow into the sump will probably be destroyed by the return pump to the display aquarium.
When adding macro algae to the refugium attempt to add a few different varieties as all may not thrive, therefore if you add more than one variety at least one will grow. Periodically you will need to harvest or trim back the macro algae. Harvesting the macro algae will encourage new shoots to grow and prevent any macro algae from crashing or dying. When macro algae dies all the nutrients which it has consumed are released back into the aquarium which is obviously something which we do not want to happen. When harvesting the macro algae do not be tempted to feed it to any green loving fish as this will only add the nutrients back into the water using a different method.
You do not need to grow macro algae in a refugium – there are some aquarists who design a system which is purely for the different types of life which can be kept. If you do not decide to use macro algae then ensure that you provide some places for these creatures to hide, some pieces of live rock will suffice.
If you do not want to have a go at making you own [tag-ice]DIY refugium[/tag-ice] then there are those which you can purchase ready made to either hang onto the outside of the main aquarium or go below it.