Like Aart I feed mine all the same low calcium feed with Oyster Shell offered on the side. When the chicks are four weeks or younger they all get an 18% Starter/Grower. Then when that bag runs out I switch to a 16% Grower for everyone. The hens that need the calcium for egg shells seem to know it and eat the oyster shell. The ones that don't need the extra calcium for 3gg shells may eat some but don't eat enough to harm themselves. That means I don't have to worry about which chicken is eating what. I let them do the work.