I've heard of them candles every day 1-18 and left after lockdown... But the more you candle the greater risk of dropping one, possibly on others, tranfering germs and accidental flipping of egg to small side up. Be careful. Always handle eggs with CLEAN, DRY hands and never if your tired.
if in doubt... LEAVE IT ALONE. I am candling every 3-4 days until lockdown because my humidity gauge is wrong and I'm also making a video diary with my 8yr old daughter for her class. Rule of thumb is days 7,10,18... More or less as you feel. Good luck with your babies.

And thank you for the experience and advice you bring!
. That doesn't mean in the course of this year he won't bring up the idea to me! He is the reason I got my first duck, first incubator, more ducks.... So I think hate may come around!
