80 isn't bad at all.
You say "a", not "some", so I take it you had one of each? If so, just to let you know, unless they are kept in groups/schools, they get stressed out.
As for why they died, if it is a new tank setup, neons are not hardy fish, so they probably died due to water chemistry. As for it being an older setup, do you know what the pH and nitrogenous compound (nitrite/nitrate/ammonia) readings are?
