So I recently just ran into a fellow backyard chicken lady and her boss who is a Vet.... as in Animal Doctor, not Veteran. We got on the subject of calcium supplementation and they very strongly advised me not to give oyster shell because it was ground from some washed up shells and full of mercury and other toxins, she uses mashed up Tums to supplement the calcium. I have switched over to the Tums, all I can find is peppermint flavor, although they don't seem to mind and it hasn't affected the taste of the eggs but it seems odd to give them flavored stuff and is pretty pricey. I am an artist and have ceramic supplies on hand and I have a bag full of straight up Calcium Carbonate, which is the main ingredient in Tums. Does anyone know if that is OK? It would be easier to just sprinkle some Calcium Carbonate in their feed then to buy Tums at the market and crush them up. I just want to know if anyone has a clue... Thanks.