Every tank could use a refugium. Try filling it with mangrove shoots, they're really good for nitrate export. As to your other question a sump is normally used in place of a wet/dry. It is basically a tank that holds the protein skimmer, the return pump, and your biological filtration (LR is the best for this. If your given a choice, choose that over bioballs, less work in the long run). Some people incorporate their refugium into a chamber in their sump. Some people also run both a sump and a wet/dry, sometimes turning the wet/dry into a refugium. 
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55gal,216 watt Tek T5, 45#LR, 45#LS, 3 maxi-jet 900's on a natural wavemaker timer,phosban reactor, 5 gal fuge (built out of standard 10 gallon tank) with chaeto and feather caulerpa, sealife systems protein skimmer, wet/dry, 3 blue/green chromi, 1 skunk cleaner shrimp, 1 coral beauty,1 scopas tang, 2 false percs, 5 mexican turbo snails, assorted dwarf blue leg hermits, astrea snails, and nerite snails | 
Wet dry filter\ refugium 
