One of my girls out of the 7 has really weak egg shells. Like i'm talking crumble in your fingertips when you try to pick it up if the chicken hasn't already broken it when laying or the next girl that sits on it. The eggs are white and very noticeably different to the brown shelled eggs of the others. I have crushed shell grit on offer at all times and I dry and crush all the used egg shells and throw them back into the coop. I also give cheese as a treat. I'm just not to sure what else I can do. Do I need to try and identify the chicken and supplement her some how with extra calcium. I am presuming it is calcium that is the problem. Or is this something not really treatable? I must say trying to identify the chicken will be hard as i'm not home during the day, so getting in their after they lay is difficult.