It's so sad, but it does happen. I have seem what looks like Columnaris on an ADF that died. Another couple from bloat/dropsy. Yet another from weird bumps. I think they're highly susceptible to diseases. Poor little things. I always feel terribly responsible when they die, even though I'm not responsible. Human condition!
Ok... video one.... i recognize the sound/music. Have it in my music library, but can't remember how to find it! Video two: please tell me why your ADFs are so active. Mine don't play. They sing and try to breed, without results.
Singing and trying to breed is probably a lot of work for them! lol I think mine just appear to be more active, but they're really lazy. When I'm around and switch on the light, they think they'll be fed. The floating pellets also help, but when I check their tank at other times they're usually off sleeping somewhere and can't be seen. Oh, and the song is "People Got a Lot of Nerve" by Neko Case.