What is a refugium for?

[Lund]

I have read about these in other threads, and was wondering just what are they exactly for. Are ther for fresh or salt water? Or both? Can you explain this to me, or even point me to another website that explains refugiums. Thank you.

 

[johno27]

I have mainly seen them used for saltwater. To my understanding they help to keep Nitrates at a very low level for coral keeping by keeping helpful algae and plants(that may be eaten by tank inhabitants) in a separate container from the main tank resembling a wet dry. The main difference is that you have to light a refugium to keep it healthy.

Here is a very helpful page for you witch i am about to read myself

http://saltaquarium.about.com/cs/aquariumdiy/a/aa041400.htm

P.S where about in MI are you from?