How to specify the database to use?

I am using two databases; a local copy of mysql which works great with GC. I plan to use AWS' RDS Postgresql for the images for use with Image crud. I have opened two databases using:
          $DB1 = $this->load->database('default', TRUE);
          $DB2 = $this->load->database('postgres', TRUE);
Default is using the mysql and that works fine. How do I tell Image Crud to use $DB2 instead? 