to avoid this problem you can set up rotation job instead of custom which makes the software more automated and even you forget to remove the tapes which are been backed up, job will pick up a different tape instead of a tape always been picked up from specfic slot.
you can go with any of the combinations avaliable depending on your requirment under schedule tab of a backup job and select a media pool which has retention time for media to make sure that tape is not over written by the job which makes the job much simpler.
second idea would be going ahead and creating groups for each day job if you are running same job every day and this is more of a non automated process and requires more number of jobs unlike rotation but this will make sure appropriate tapes be picked when backup job starts for that respective day.
