You already had one thread open on black skirts so no need to start a new one for future reference. Breeding should happen naturally giving the right enviroment. The ideal would be on their own in a healthy planted tank with soft, acidic to neutral water so an ideal ph 6.5 - 7 with low nitrates below 10 for the best chances.
They will also breed in a community setup. The water chemistry is important regardless so soft acidic water is definitely needed. Make them feel safe so keep disturbances to a minimum.
My tetra used to enjoy spawning in morning sunrise.
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Fish die belly upward and rise to the surface. It's their way of falling.