Only because I'm silly, what day are your eggs on? Because you "can't see anything" doesn't mean that the embryo isn't doing it's thing. I don't know about anyone else, but I only candle once - just before lock down. The reason I do this only once is because the egg shell is so thick, it makes seeing veins very difficult. I have taken a chicken mcnugget lid, traced a dime on it, and cut out the circle. When I place the egg on it, the egg would sit right on top of the hole as I shined an LED flashlight through. The first time I tried candling an egg it was translucent on day 7, and the blotches on the egg make it difficult to see any veins. On day 14 (for pharaohs), any eggs that are completely translucent are tossed, and the others kept in the incubator. I hope this info is of some help.
James