What fish eggs are too sensitive to hatch?

[francois]

I got Corydoras aeneus (Bronze Cory), who spawn. I took out the eggs and hatch them in small container with methylene blue. Everything was fine and got a fairly high hatching rate.
Last year, I got few spawns of Cory orange laser. I took out the eggs and add methylene blue. Very few did hatch and out of the few, most if not all died soon after hatching. I change the dose, I switch from Methylene blue to Acriflavin at different doses but the rate was still very poor. It was not a male fertility problem as unfertilized eggs turn white within 24 hours.
Did you experience such things with your fish and what were they?

[GaryE]

Often, it is the mineral content of your tapwater being very different from the mineral content of the waters your fish evolved in.
When I kept a lot of Apistogramma, I found eggs from one species would hatch easily in water that another species' eggs would die in.

[francois]

Thanks Gary for this answer. Do you know by chance is the change in water hardness has an effect on the shell of the eggs or if it affects the embryonic development. I cannot really find any test and or study about it. Maybe with your broad reading of aquarium literature, you came across something that do address it.
In the case of my corydoras, the eggs were incubated in the same tap water as the parent have spawned. Just that these eggs are very sensitive to bacteria and or fungal infection, plus they were not happy at all when incubated with a bacteriostatic agent like Methylene blue or acriflavin.

[Fores41]

I have had the same problem out here as my water is very hard 530+ppm so I use RO water or distilled to mix with tap water. For any Cory I would use RO water or distilled and if you have as soft as Gary try for a 25-50 ppm water hardness for the lasers and see what happens. I know that Amazon water way species struggle for breeding in our harder water as the eggs take on to much minerals while developing.
Nice thing about distilled water is it is Sterile until mixed with tap water.

[Biulu]

I know that Montrealapisto is using some sort of egg hatcher/tumbler that keeps the eggs suspended most of the time due to the air blown through the device. Are you aerating your eggs a lot or only moderately?

Apparently this improves hatching and survival rates a lot. I once made this device from a coffee filter which kept the eggs moving constantly as well:

DSC00924 by Biulu, on Flickr