Hello, My girls just started laying (today!). They're 8 months and have been on an organic layer feed since they were 6 months. I have never given them grit. Their run is sand and clay/dirt. I do give them fruits and vegetables a few times a week. Do they need grit if there is sand in the run? It's kids sandbox sand. Also, do they have to have oyster shell? Do you just mix it in with their feed? Thank you!