I've got 4 hens - 1 2yr old BR and 3 1yr old RIRs. For the most part they're fairly productive as I generally get 3-4 eggs each day. In the past 5 weeks I've been getting an egg that has an extremely soft shell. It's one hen, (I suspect one of the RIR girls) because she always lays in the same box and she is the only one that lays in that box. The other eggs I get have very thick shells. I've been adding crushed oyster shell for the last 3 weeks (in addition to BOSS to encourage them to eat from the coop and not just what they find outside). Someone is certainly eating from the food dish in the coop, however, her eggs are still thin. I went out tonight to collect eggs and while holding an egg and trying to close the coop door it crushed - frustrates me, but my dog LOVES it! Anyway - am I not adding enough oyster shell? (I add about 1/2 cup each night.) Or do I need to give it more time to work? The strange part is that she, and her sisters, have been laying since last October and the problem has only flared up 5 weeks ago and it's just her. How is it that only one is not getting enough calcium when they're all exposed to the exact same environment?