What's the smallest functional refugium?

[yosemite sam]

I am looking to set up a refugium for my 20 gallon reef to cut down the nitrates. I saw broomer's illustrations of a "ghetto" 'fuge and think that is the way I should go. I have limited room under the stand and was wondering how small a 'fuge I can make and still have it do what it's supposed to.

 

[frankl15207]

I have a 2 1/2 gallon CPR hangon and a five gallon coming off of my sump in a 75 (lack of space under the tank - needed to custom build it to fit) and my nitrates rarely go above 10. I would say with a 20, you can go small and still get good results.

 

[mr . salty]

I wouldn't suggest anything smaller than a 10 gallon,Much smaller than that and you are really limiting it's capasity for sand,rubble rock,and algae.These are what make a 'fuge work in the first place.
The general rule here also is "THE BIGGER THE BETTER"