HI,
A refugium works just like a sump only w/ a fuge in the middle. Typicaly they are DIY and made from a standered long tank or cut and glued acrylic. They are divided into 3 chambers w/ sets of baffles which are 3 pains of glass to make all the water flow over the first baffle, then under the second baffle and over the third into the next chamber. The first chamber is where the main tank drains to from an overflow befor it goes thru the first set of baffles to the fuge chamber. Any equipment like skimmer, UV ster. ect should be in or pump from the first chamber. The 2nd chamber has a deep sand bed and small LR and plants wher micro life can thrive, pods ( small buglike crustations ) worms, snails, mysid, stars, ect. This life helps filter ( eat ) leftover food, ect. from the water. It also will get sucked from fuge and into MT thru main return pumps. This provides a variaty diet for fish manderines, butterflies, ect. and keeps them healthier. You can also place filter sponges in the fuge to collect pods and then shake them out into the main tank. The plants like calaripa and others help to absorb the nutriants like phospates out of the water so nuisance algea like hair algea, ect does not grow so easy in the MT. The fuge area will need a light source for the plants. From the fuge, water then flows thru the last set of baffles to the pump chamber where it is pumped back to the main tank. There are many veriations from this typical design but this is ment to be a simple explination. Hope it helps and does not confuse.
This is not a good pic but this is my fuge. I have bioballs in my fist chamber and the pumps are to the right and cant be seen.
