The shell strength is determined at least in part by the diet. Although not a rule, the Ameraucanas I've seen are often more passive and therefore lower in the pecking order, which means they don't have as good a diet. Giving a chicken calcium (and magnesium) is probably beyond the scope of this thread, but it becomes increasingly important as the hens age.
Our chickens are somewhat spoiled. We use organic lay crumble ([Invalid or Expired Link Removed] in our case). It doesn't cost much more than regular feed and I think they actually eat less (being more satisfied perhaps).
I haven't really been supplementing their diet beyond crushing up their egg shells and putting them into the compost pile next to the coop. Only the one Ameraucana lays the fragile eggs. They eat a half bag of laying mix a week, but they follow me around as I tackle landscaping projects and feast on everything that turns up. They also hang around the back door and eat sandwich crusts and other scraps that the boys throw out. I saw one of them running around with a mouse hanging out of its beak yesterday and another one was eating a little snake last week.
How big is your operation?
it was a massacre of legendary proportions! feathers & blood everywhere! 

