We have a flock of 17 hens that are 9 months old. We feed layer feed and supplement with oyster shell, scratch grains and collards or some other leafy green veggie. I have noticed an occasional cracked and sometimes broken thin shelled egg in the nest boxes. I don't know who is laying them. We also have some eggs that have lumpy calcium deposits on them. So my question is, if the egg that has the thin shell is due to lack of calcium, how do I supplement with calcium without overloading the hens that are laying the eggs with the calcium deposits on them? I am afraid that if I don't do something about the thin shells, my hen will end up with egg yolk peritonitis or some other infection from getting torn up by broken shell. Any suggestions?