We're putting the babies outside sometime this week, and I was wondering if it would be safe to give them granite grit yet. I've heard there's calcium in it, and that it's too big for baby chicks. Is it small enough for six-week-olds? And will it hurt them to give whatever calcium is in the big girl grit? One reason I'm wondering if we can switch to granite grit is because the pet bird grit we've been giving them, although it seems to be doing it's job, it seems as though they certainly go through quite a bit of it. How much grit should I be expecting them to use? Thanks!