We have 4 hens that just started laying about a month or so ago. They have constant access to oyster shell, plus I give them yogurt every day and recycled eggshells once or twice a week. Still, two of them have a recurring problem with soft shells, and it seems like they're not eating the oyster shells much at all. On top of which the hot weather has them eating less feed, so I know they're not getting enough calcium. Today I ground up some Tums and mixed that with their yogurt, and at least they ate that with enthusiasm. Any other suggestions?