Hey gang, I have a small flock of mixed breeds, RIR, Wyondottes, New Hamp Red, Americuna, 10 hens and a rooster. Ages from 1 year to maybe 4 years for oldest. I'm having an issue with fragile eggs 1 to 3 a day, I get a total of 6 to 9 eggs a day. Feed pelletized 19% layer feed and free choice oyster shells. 1 cup of scatch shared by the flock per day. Occasional, vegetables, and yogurt. 10 x 10 chain link run opened most afternoons to allow free range, no apparent stress. What can I do to improve egg shell construction?