To breed neons or cardinal tetras you need very soft, and acidic water. The PH needs to be around the 5 mark,Less than 3GH and Kh under 2.Feed the females lots of live foods in the breeding tank when you see the females starting to become heavy with eggs put the males in with them. Lots of thick fine leaved plants and a trap in the bottom of the tank that the eggs can fall through so the parents can eat them. It can be done but it take a lot of patience and some experience.