Hello We recently decided to start (2 weeks ago) feeding our chickens crushed up egg shells as a source of calcium, they're around 20 weeks old and are expected to lay soon. Our questions as listed: -Should we continue doing this? Does it have an effect? They seem to be eating it. -Should we worry that they eat too much of it? How to prevent this? -How much should we be putting out? -How to keep it water proofed, without having nasty dirt and other stuff getting inside it. Thanks for any help! If you need more detail I'll be happy to explain.