The tank is a bit young yet to put something like a mandarin. I would wait just a bit longer to put more fish in there, especially it just got done being cycled. I would personally get a Tang (small) myself cause it would give it time to grow. But eventually it does need a larger tank to go in. I personally have two small tangs in both of my tanks, a Yellow Tang in the 46 bow front and a Naso Tang in the 55....It's just something we started with and once they do well in both tanks, we're getting a 125+ gal tank in the spring to move the tangs into. We're just gonna check into the paper to see the best deal, missed a deal for a 180 gal tank with all setups, canopy lighting, and LR + 8 fish for $1000 Won't have money for the tank til spring...The Yellow Tang is growing pretty big so can't wait til spring for a larger tank to move her in...Whatever you decide to do would be fine, but think of their future too, it's just my personal opinion...Good Luck!!!