Neon tetras are difficult to breed. I believe how you breed neons is to set up a separate cycled tank with a sponge filter, java moss, and marbles as a substrate, all in a dark corner of the house. The water should be slightly softer and slightly cooler than the main tank. They will not spawn in any water that is higher than 7. Acclimate a group of neons into the tank and keep it dark until night. They should spawn in the morning. After the females look skinnier about 24 hours later, remove them. The eggs are nearly invisible so you can't really see them. They should fall between the cracks of the marbles and in the moss where they will lie safely for 22-26 hours before they hatch. Make sure to buy them special fry food