refugium is a place with *typically* a DSB
and some Macro to export nitrites etc and to put a little love into your water, it also gives a place for pods
with a fuge, you kinda want to light it opposite of the tank and then it can also help your pH swings during the night to day.
all-in-all a sump just adds water volume, but lots of people including myself put extra equipment down there.
I have my skimmer, a heater, and an extra 30# of liverock
75g w/ 30g sump, 160# LR
, 60# sand: Inverts =18 turbos, 30 nassirus's, 40 blue leg's, 5 emeralds, 1 CBS, 1 skunk cleaner, 1 brown gulf shrimp? and various other LR
hitch hikers yet un discovered or un-ID
Fish=1 yellow tang, 1 yellow headed jawfish, 1 pink/blue shrimpgoby, 2 perc clowns.
Future fish = 1 sixline, 1 lawnmower blenny