My chicks are going on 6 weeks old and doing very well. I'm just about finished with the coop and will put them in it by the time they are 8 weeks old. My question is, the run they will be using is has a total rock dust bottom to it so I'm thinking they will have all the grit they need. I'm just afraid they may get to much of the grit. I've heard of impacted crops and was wondering if they can eat to much grit, especially when their not use to it?