Your QNAP fills up faster than it should, and you suspect the same files are sitting in several folders. Phone backups, re-downloaded videos, copies of copies. You'd like to see them and clear them, but QTS doesn't make that obvious, and the tools that exist each cover only a slice of the problem.
What QNAP actually gives you, and where it stops
For photos, QuMagie has a Similar Photos feature. It's useful, but it's photos only, deletion is manual, and it doesn't reliably re-index afterwards. For storage, QNAP's deduplication (QuDedup in Hybrid Backup Sync, or block dedup that needs a lot of RAM and only on certain models) shrinks how data is written to disk. None of these gives you a plain list of which files across your whole NAS are duplicated, so you can look and decide. For everything that isn't a photo, there's no built-in answer.
The usual fallback is the command line
For videos, documents, archives and downloads, QNAP owners typically end up with fdupes, jdupes or a dupeGuru container, run over SSH or Docker. These work, but there's no preview, no clear view of how much space you'd save, and one wrong flag can delete the wrong copy. That's a lot to ask for a routine cleanup.
What NAS Ranger does instead
NAS Ranger connects to your QNAP shares over SMB and finds duplicates by content, not by name, across every file type. Identical files are caught even with different names, dates or folders, and two files that merely share a name aren't flagged by mistake. You see every duplicate group and the exact space you'd reclaim. For the detail of how content matching works, see how to find duplicate files.
Clean up in bulk, without deleting in place
You act on hundreds of files at once from a clear interface. Nothing is removed permanently in one click: confirmed duplicates are moved to a trash folder on the NAS, a rename that's instant even for big video files, so you review before you purge. Here's why that stays safe. And because NAS Ranger runs on your computer, there's nothing to install on QTS and a firmware update can't take it away.
Try it free: scan your QNAP, see every duplicate and the gigabytes you can reclaim, before touching a single file.