With this set up I can clone with my default key as Bitbucket suggests:
git clone [email protected]:username/project.git
If I want to clone a repository from my second account I can alter the command to use the second SSH key I generated:
git clone git@bitbucket-accountB:username/project.git
Source: http://dbushell.com/2013/01/27/multiple-accounts-and-ssh-keys/