55-gallon tank with wet/dry filter system

[stephen1_fergus]

I have a 55-gallon corner tank with a wet/dry system that I am coverting from fresh water to salt water (reef tank). I was told that it is good to take the balls out because of the nitrate pockets that can form so I did and now the system sounds like a very loud waterfall. how can I quite it down?

I have been hearing things about a "refugium" that can be setup in the filter system. What is a "refugium?"