I have 3 week old chicks that I'd like to give occasional treats to and I know I need chick grit. My local feed store is out, so here are my choices... regular grit (which I believe will be too large), bird gravel (local petshop I called suggested that product) or just sand? Which is the best choice? I realize they don't NEED anything but their starter feed, but I'd like to give a few treats to help me bond with the chicks... Thanks in advance for your help!