This is my first time hatching eggs - we have duck eggs under a broody hen. It is day 21. We candled the eggs tonight and they were definitely moving around, but one of them seemed to have an air sac larger than the other - taking up about 1/3 of the egg. It is one that we discovered a hairline crack in a few days ago - we covered it with wax and it's been holding up well - still moving around 3 days later. Is it normal for the air sac to be this size? If it is not, is there something I can do about it? Also, after we candled tonight I saw something about keeping them on lock down when it's near hatching time - I am guessing this means I should not be candling anymore? Is it bad that I candled tonight? I am so ignorant regarding this as it is my first time. Any help is appreciated. Thanks!!