Additional Fish/crabs/shrimp To The Tank

[jpool10]

Hi

I've read the post by OscarWilde about the Blue Lobster and was wondering this. I already have a red clawed crab in with my blue lobster. Will it harm to put another one or two in the tank or am I endangering them and/or Bob (my Blue lobster.....which having read OscarWilde's notes I now thing is a girl!! hmmmmm)

Thanks for any advise

Jo