man that sucks hate it when fish die and other are just fine, especially something so small and cute. hope you able to find them again and have beter luck
I lost 7 really nice medium size Blood Parrots to a water Change in 24 hours all at once when all the other fish in the tank diden't bat an eye, and only after months of research and trial and error did I discover the cause and now keeping them again successfully, its a local water issue so the details aren't important here, what is important is that we can learn from these errors and avoid them or at least minimize their impact in the future.