I dont think finrot in itself kills the fish, but leaves them at the mercy of other infections. If its early finrot treat with Mefalfix for minor scrapes etc, if its past that interpet do a specific treatment for finrot.
make sure your waters good though, I usually find finrot, bladder problems to be water chemistry related.
melafix doesn't stop finrot, it only helps heal it, aquarium salt can help heal finrot too, also to stop it spreading further doing salt dips can help endlessy....if you want to know how to do these let me know!
Finrot can only kill the fish if it retreats all the way to the body, because the fin tissue can not regrow from there.
Is the fin black round the edges, or is it falling out in chunks or fraying?
Ah weird....normal fin rot shouldn't kill fish as people have said, sounds like something else is going on.....just for finrot though in the UK myxazin and melafix is good, pimafix and melafix has also halted finrot for me, but my fishes fins were dropping out in chunks
in the US i've been told maracyn one and two is good.
But it sounds like something else is going on there, they shoulnd't just be dropping dead like that