Sorry, no tangs in anything under 75g. Even as juveniles they require a lot of swimming space. You'll come to find as you get more experience that there are a lot of LFS and online vendors that don't know what they're talking about, and are willing to give you false info to make a sale.
You pretty much have to not take ANYONE's word, (including mine), about anything. Check several sites, read books, and magazines and you'll start to be able to weed out the idiots, based on communal knowledge.
This is by no means a complete list, but it should give you something to look at.
FWIW, I totally disagree that twinspot gobies are a good choice for a nano. They tend to be finicky eaters and prefer to sift the sandbed for their meals. A nano simply doesn't have enough life in it's small sandbed to keep them alive long term. But like a few other fish, if they take prepared foods in the store they might be good choices after all, there are always individual fish that are the exception to the species rules.
http://www.liveaquaria.com/product/scat ... CatId=2124
B