I have hatched many eggs, I have never had mold or mildew on the eggs. Can you clarify, is the mold or mildew inside the egg and you can see it when you candle? I have had that happen to me and it appears to be a bad egg, one that was too old. So i cracked it opened and BOY was it a stinky little one. So if you are seeing the mold or mildew inside the egg chances are it's no good. If it's outside the egg, mmmm, perhaps your readings are off, What is the temp and the humidity at? What kind of incubator, a homemade one, a dry one?? Need more information... sorry..