Howdy! My 2 babies are almost 19 weeks old and i was wondering some things i appreciate all questions being anwsered!thanx 1. when do I give them layering feed? the bag says 18 weeks but the start and grow says 20 weeks plus i have more start and grow and wanted to get rid of it... 2. Do I give the Grit AND oyster shells? 3. How much oyster shells do i give them? 4. I hear you can mix them, but I wasn't sure how much to mix.(should i get another feeder of oyster shells?