Skyrocket, I am sorry that all your fry died suddenly - and I am wondering what might have caused it.
Fry die easily, that is just a fact. They are fragile things, and they are affected by things that a bigger fish wouldn't be bothered with. Did you do anything different, anything unusual in the feeding maybe, or the cleaning? How often did you clean their tank, the bottom, and was there a filter of some kind in their tank?
A massive die-off like that sounds strange. Yes, a larger number of fry seem to be dying every now and then, but all of them basically overnight sounds suspicious. Maybe something got into their tank? Windex? Any kind of insecticide?
I am just naming the things that come to mind, maybe you think of somethin that might have been off lately. Sorry again - I know how hard it is to lose all your fry like that, especially your very first batch...