Hi new to chickens but have four Hyline hens. Two (purchase in Aug) lay beautiful eggs. The other two (purchased Feb at 18 weeks old) lay eggs with shells either broken (or usually break picking up) or are just membranes. The eggs have been like this since just after I bought them. Their feathers look a bit duller than the two 'good' chickens. But they otherwise look very healthy. I feed them high quality food and have tried different types. There were allowed to free range, but have kept them cooped up for the last month to see if this would help. It hasn't. They have free access to poultry grit. They lay almost every day. I would LOVE any advice on what to do. I am sick of cleaning messes out of the chicken house! Thanks so much for reading! P.S. I'm sorry if this is in the wrong category. I wasn't sure if it due to disease or nutrition!