my chicks are a week old and are devouring their grit. the organic feed they are on is finely ground but it has some medium sized bits in it, so i've been giving them grit in a separate container. they have gone through a whole 24 oz box already! can they eat too much grit? if it isn't unsafe, i don't mind buying them all the grit they want, but i don't want to accidentally hurt them.