I have noted that when the sand in my run disappears under scratched up dirt and the inevitable bird waste, the egg shells seem to get soft, so I can break an egg just in a gentle bump while carrying it in the house. It is more obvious if I offer oatmeal as a snack - so one of their favorite treats has disappeared, maybe to return if I find a calcium supplement (could I crush up my calcium citrate w d3 and magnesium and add it to oatmeal or water?). One egg laid the day after an oatmeal treat had no shell at all, just the inner membrane. I never supplemented calcium in the beginning, didn't need to, I feed Layena, the eggs were good with good hard shells, and as long as they only eat Layena, and the run has fresh sand, the egg shells are solid. But hens do like treats, I don't eat or buy dairy usually. I've been in such an egg dearth due to heat and I'm assuming imminent molt, that I bought eggs at the store last week for the first time in a year. And those shells are definitely harder than my hens. But then those would be the eggs that survived machine handling, hmmm... I offer swiss chard when I have it, broccoli when I have it. Romaine lettuce when I have it. (drought has nailed these in the garden), all have some calcium in them. They are presently having leftovers and melon for snacks, plus whatever bugs they catch free ranging. Today they got leftover roast chicken, torn in little bits, because I had about 3/4 of a cup of it, and they need extra protein if they are to lay eggs at all. Any tips? Or should I go buy some of those bird calcium blocks for them to peck on?