My hens are right at 6 months old. They have just started laying there first eggs. I have noticed a few of the eggs have very very soft shells.I am feeding them Nutrena layer feed. The guy at the store said I didn't need any type of additives since it was a complete diet for my hens. Is he wrong? Is this a poor diet for them? I really want them to be healthy but I also want delicious healthy eggs!