Jessica,
Which version of BIG-IP are you running? If you are using 10.x, you will need one monitor per RAC node as described in our "Oracle Database and RAC" Deployment Guide (http://www.f5.com/pdf/deployment-guides/oracle-rac-database-dg.pdf). If you are running version 11.0 of our software, the monitor has been simplified and you will only need one monitor per RAC; it also allows for a free-form Connection String.
If your problem requires more urgent attention, please contact Support or your F5 Sales Engineer.