I am in the same situation and plan to do what Cats Critters suggested. My hens are currently on layer and have Shell free choice. Despite the calcium content of the layer feed, they actually do still eat a little shell. I anticipate that their shell consumption will go up once they are back on Flock Raiser but it will only be for the 12 weeks or so that it takes the younger chicks to be laying and able to switch to layer again.