Hubby just called me from the store and asked what I needed for the chickens. Oyster shell is on the list, but they only have 50# bags for $11.00. I told him to pick it up. I have 3 pullets that are 17 weeks and one is getting ready to lay. How fast will I go through the oyster shell with eventually 8 chicks? How long is the shelf life? Is it like DE and pretty much last forever?Thanks.