My hens have had pretty bad calcium deficiency problems for a while. None of them are old and they have oyster shell free choice. I had the brilliant idea of using vitamins instead of oyster shell which doesn't seem to be working. I went to Wal-Mart and bought a bottle of Calcium vitamins. I put the tablet in a cup with a small amount of water. Let it dissolve completely (about 3 hours) and then poured it into their waterer when I was putting fresh water in for the day. Filled the rest of the waterer with water (of course) and called it a day. I did this for two days, and I was only getting 2 eggs a day with 19 hens, now I'm getting 4 eggs. I'm going to drop the vitamin water down to once a week and then later to only once a month for maintenance. I have a few sick chickens that I'm nursing, so I also got a bottle of Vitamin C and put one tablet in with the calcium as well. Everyone seems to have a little bit more energy and is more alert. Hope this helps!!!