Spotting a fry may be to late. I have seen the larger ones eat the fry quickly after being hatched. When they females stop eating check their mouths for eggs, roughly 18 days from last hatch. Hatch the eggs yourself and raise separate from the larger ones.
When the water starts becoming cloudy is when they will start dieing off. Don't really know what causes it. I have run my tanks from clear, green, real dark green and almost black with no problems. When it takes on a cloudy tint, problems.
