Hi Everyone, I'm new to this site. We bought 6 chickens 3 months ago who were already laying and are about 2-3 years old. I think.. I free range them in our fenced in back yard, they have about an acre to roam on with plenty of shrubs, bushes and trees to forage through. I feed them oyster shell and an organic corn-free layer feed with plenty of water with a little bit of apple cider mixed in. The main issue I am having is that my Americana (who lays green eggs) the shell is thin and rough with calcium deposits on them, my other chickens' eggs have thin shells as well, with no calcium deposits but are now starting to form hairline cracks and little wrinkles. I can't seem to figure out what the issue is and how to fix it. Are my chickens too old? Please help!