Breeding South American Tetras
There are several hundred species of tetra. Not all of them breed in the same way. A few of them that have different breeding patterns are: the Splashing Tetra which lays its eggs out of the water, the Rummy Nose Tetra which can be made permanently sterile by calcium ions in the water, the Glass Bloodfin Tetra which likes harder water than most South American tetras, and the Emperor Tetra which is not a strongly schooling fish. As well as these, the tetras vary enormously in their ease of breeding, and particularly in the necessity of exactly the right sort of water.
However, despite these differences between the different species there are some things common to most of the South American Tetras.
The tetras, in general, are egg scatterers. All the tetras I know have external fertilisation so both males and females will need to be in the spawning tank together. They need very soft acidic water. The temperature varies with the different species, but mostly they will be stimulated to breed by a small rise in the water temperature.
A breeding tank set up for tetras will be scrupulously clean. Although in nature, the fish will lay their eggs over plants, many people prefer to use a synthetic spawning medium because it is easier to clean. For breeding, many of the tetras require water that is not only extremely soft, but also very low in total dissolved salts.
Not all tetras eat their own eggs, but the great majority will, sometimes in surprisingly large numbers in the wild. Tetras in general are also cannibalistic to their own babies. Because of these two things it is normal to remove the parents after spawning.
Tetras do not usually produce babies in community aquariums, but I have known several cases where they have done this. Naturally, they have been easily bred ones like the Black Widow Tetra.