Wow, it really worked! Listen (and see on the chromatic tuner) how improved the melodica is! I might go back in and fix my low F, but probably not for now.
I’ve used this melodica live and in recordings for several years now. I think it will go on for a good while longer now that it’s in tune!
I found the Hohner harmonica tuning video invaluable: https://www.youtube.com/watch?v=pfC9OPmhyuU
However, I hadn’t seen any video explaining how to do this specifically for melodica, so here’s mine!
1. Download chromatic tuner software from Katsura Shareware or elsewhere (http://www.katsurashareware.com/piano/piano.html)
2. Check tuning of all notes and write down deviation in cents
3. Open up melodica and save screws
4. Dry it out with a rag
5. Find notes you want to change by plinking or checking which key coordinates with which reed
6. Support the reed with a pen knife
7. File the reed at the tip to RAISE the note, and scrape with knife or edge of file at the base to LOWER the note. Only do 4-5 strokes either way.
8. Plink the reed a few times to settle the tuning
9. Reassemble melodica (power drill helps because you will do this several times)
10. Check tuning. Repeat procedure until you are happy with all/most notes! Perfection may not be attained. I was happy with any note within 10 cents of the note value.