I don't know for sure what will work. I just kind of threw everything at Myrtle (my struggling Polish). Something in that laundry list seemed to help. She's still smaller than the others, but at least she's acting like a normal chick now.
It was probably born with something that made it harder to thrive - might have been a long hatch, temp might have not been ideal for whatever reason. I don't think falling would cause slow growth, but I am no expert.
I had one this season who was not doing well at all. She would lie on her...