Well, there are two kinds of blue lobster, the blue night lobster and the hammer's cobalt blue lobster. They both require a fine enough substrate to burrow in. The blue night will grow to a foot long and will need a tank of atleast 60 gallons, and the hammer' cobalt will grow to 5 inches and needs a tank of atleast 20 gallons. The blue night nor the hammers cobalt should not be housed in a tank with two of same species. You'd need a really big tank with lots of hiding spots, if you wanted two of any species. You can add almost any fish in a tank with either lobster, they are too slow to catch any fish. But, the hammers cobalt may try to snag fish which are small and slow. Neons, other tetras and endlers (all small fish) would be okay in my books.
liveaquaria.com is a site where you can find info about the two lobsters under: freshwater invertabrates
EDIT: grammar, spelling
