I have been feeding my chicks Nutrena Chick Starter/Grower. I was thinking that because it was called Starter/Grower I could feed until through the grower phase which I understand to be 8-20 weeks. Now I notice the bag says feed until 6 weeks and my girls are already 8 weeks! Should I switch to something else? or is this good until 20 weeks when I start the layer feed?