I try setting out oyster shell containers for the girls but they keep getting knocked over, stepped in and scattered in the bedding. Before drilling a setup in the walls for something spill-proof, I mixed a bit in with their layer food yesterday and it all got eaten well enough. Today? 3 out of 6 eggs had gritty sandpaper shells! All had been laying perfect eggs to date with lovely smooth hard shells. So, I guess my flock doesn't need any extra calcium! Has this happened to anyone else?