I feel, as long as your "blue lobster" is an Auatralian redcalw. that the tank is a tad small. i usually reccomend a tank of 20ukg (yours is 9.5 or so), for one cray.
redcalw regularly reach a length of 6-8 inches. and that does not include the claws and antenna. all in all they reach, 10-14 inches claw to tail.
I'm sorry. but i think you will need a rethink, or a bigger tank.