yeah, mihkaail is right. Don't let it discourage you though. There are so many pretty varieties to choose from. Owning a mandarin isn't impossible, but it's a lot of work to keep them well fed when dealing with smaller tanks. I should know, my g/f bought one not knowing for her 12 gallon because she loved the coloration and what not. She had an idea that they can adapt to prepared foods, but of course....guess who had to do all the training? ME! lol. Well I can say the mandarin is doing fine, and his belly is remaining full, but it took a while for me to get him to accept mysis, cyclopeeze, and brine shrimp. As for brine, if you have baby brine, it does have nutritional value, but if you have adult brine, it's true, they are not nutritional, and it's basically like eating candy, but what you can is have them soaked in enriched vitamins that make them good to eat, like soaking them in "selcon" i believe. So there are various ways to help adapt and care for the little dude, but as you can see it's a lot of work, and I always have to spot feed the mandarin to ensure the "mandy" is gettin' her fill.
Anyway, great starter fish are clowns, and better stronger survivors are the Ocellaris Clowns (NEMO). Assorted gobys like the neon goby, red headed goby, yellow striped goby, are tiny little guys, like guppies, and easy to care for. Ones with really pretty coloration are the firefish species. Careful for those, if you dont have a closed top, they are indeed jumpers, so that's one thing I'd look out for. Well I'll leave things at that, let us know what you end up getting and be sure to post pics! Best of luck!