Found this from a google search.
Don't have any actual experience, sorry
"Breeding Congo Tetras generally requires a large, well-lighted tank with plenty of swimming space that is at least partially planted. Goe Gallon noted that the ideal water should be soft and slightly on the acid side, and that filtration through peat may be beneficial to encourage spawning. He also noted that spawning temperature is best between 25-27 degree C (75 - 77 degrees F). Prior to breeding, a pair of Congo Tetra should be ideally conditioned beforehand with ample feedings of live or frozen foods.
During mating, the male will actively pursue the ripe female until between 300 - 500 eggs are laid, generally in or around plants. These eggs are only weakly adhesive and it is common for most of the eggs to sink to the bottom. At this point, it is recommended to remove the parents once the eggs are laid as the adults may eat the eggs or new frys. The eggs should hatch after an incubation period of approximately 5 - 7 days."