One of my EE is laying eggs with very weak shells. They break easily with little pressure. All other chickens are laying normal eggs. They have access to oyster shell and my son's sandbox sand. What else can I do for her? Thanks!
She may not have learned to eat the shell grit. Or she may have an intestinal upset or worms stopping her from absorbing nutrients properly. (Dirty water or water with algae in it are precursors for egg problems.) Not saying that's the case here, these are just some possible causes.
All you can do at this point is get some extra calcium into her. You can buy soluble vitamins that include calcium or you might be able to add extra calcium to the general feed and hope that she gets her share.