Your best bet is to contact the admin you dealt with by email. just email adminname@reefcentral dot com.
If you don't remember the admin's name, try the feedback forum,
http://www.reefcentral.com/forums/forumdisplay.php?f=74
RC generally doesn't want people opening multiple accounts and they will deactivate the new accounts when they find that has happened. Just work with them. As long as you're not trying to get around the rules, they will work with you.