Why are my fry dieing???

[flush_of_fate]

My black swordtail gave birth to about 30 fry about 3 or 4 weeks ago. Then about a week ago around 20 of them died within 3 or 4 days. I never figured out why so I figured I would get back on here and ask.(this was my first time of trying to raise so many fry so I don't know much about it)

 

[Tokis-Phoenix]

What are and were the water stats like ammonia, nitrate and nitrite like in the tank when they died?

 

[Tolak]

Fry tanks need cleaner water, requiring more water changes than a tank that houses adult fish. Some livebearers are severly inbred with attempts to get a certain color pattern or fin configuration. If you have had fry from this fish before, I would suspect the water. If you haven't, and are keeping up on water changes, I would suspect genetics.

Tolak