I have Red Stars that are six months old. They are laying normal looking eggs, but I would like the shell to be a little bit thicker. If I scrub the eggs slightly too hard while cleaning they will easily break. Also, if I hard boil the eggs the shells are hard to remove because it stick to the egg whites (I try removing at different temperatures with the same result). I feed them 16% layer pellets. The occasional snack they get are usually cabbage, watermelon, sprouts, and apples. Is there something I could feed them, or maybe add to the water that would help supplement what they need to develop better shells?