Unless you have selected to trim catalogs, the \Catalogs directory will continue to grow as long as new tapes are added.
When BackupExec re-uses a tape, it should delete the old catalog file, so if you don't add new tapes, the directory should be fairly constant after a while.
In your case, sounds like moving the catalog directory would be the easiest, since it doesn't require a re-boot, just stopping/starting the BackupExec Services