A Mandarin Goby? Or as it actually is called a Mandarin Dragonett, they can totally be in a smaller system, especially if you get a real good one that was captive bred, and you can get to eat, with supplement of Pods. I too was worried about it, but one of my LFS gets awesome Mandarins that do great in any tank. My nephew had this dude since February so far, and he is fat and happy! Thanks
@EeyoreIsMySpiritAnimal for the help here.
Trust me I know all the myths surrounding these dudes, but lots has changed, If you can find them from an LFS that gets them from a supplier and they are already eating some food, you have a great survival rate chance with them, again supplement with pods in the beginning...but eventually they do just fine.