How to get rid of duplicates

As clearly stated by Greg, the organizer is a very serious tool to 'prevent' the creation of duplicates; it's not a 'miracle' solution to find them, whether real duplicates or visual duplicates.

The organizer will not and can't find duplicates on your drives if they are not in your current catalog.

So, imagine you use one of the many duplicate finder softwares outside of the organizer, you'll have the choice to delete or move the unwanted dupes. In any case, that will create 'missing' files in your catalog, and you'll have to run a search for those missing files and delete them from the catalog.

If you use the visual tools offered by the organizer to find visual dupes (for instance original+versions, or various sizes or crops) then you'll be able to 'stack' those items for easier and faster searches. Which item of the stack do you wish to keep or to delete? Set one of those as the 'top' of stack; if you have time later, you can choose another one or delete the unwanted dupes without creating missing files. If only the top of stack is interesting, just 'flatten' the stack, that will delete the other dupes.

About albums:

Albums are only sorted lists of files registered in your catalog (sort of playlists). The issue with deleting files from disk is to do the deletion from the organizer, not from external tools or the explorer, which would create missing files.

What do you mean by duplicates?  The Organizer does not normally allow exact duplicates of image files to be imported.  If you mean visually similar images, try one of the options under the Find>By Visual Searches menu.