I kept a Zebra Lobster for over 1 year in my twenty gallon with cichlids...the peaceful ones, like 1 severum, 2 keyholes, and 1 blood parrot....No problems, but if you give introduce a blue lobster to a tank with some of the more aggressive ones, like firemouths, convicts, dempseys, etc. the lobster will be destroyed, as I found out when I tried to put a 2" blue in a tank with 2 convicts, 1 texas, and 2 firemouth...
Also, blue lobsters get sort of big, 5-7", so plan on that as well...If you want a lobster, try a zebra lobster, mine was extremely active( he used to climb the plants to the edges of the leaves, without tearing them!, and wave his claws around!); he virtually ruled the aquarium! Plus, they only grow to a max. size of 4", which is perfect....
Also, get som pellet food, like shrimp, that sinks to the bottom quickly so he can feed...Plus, for housing, find two rocks, from a garden or construction site, clean them, and place them in the tank forming a cave...They like to hide about half the time so they need something all their own...One last tip is to give the pelelts after feeding flakes to the fish, as they will consume the pellets as they sink to the bottom.