I am not trying to fuel a debate, but I have asked this question from a few different people on this board. The consensus seems to be no smaller than 180 for the full life of one BB shark.
Elkhntr is right, dont go any smaller than a standard(6'x2'x2') 180g for a full grown bamboo shark(the reason I say this is the foot print of the tank). CBSHARK's sharks are fine for now since they are both far from full grown.