I purchased 6 baby chicks from Tractor Supply 3 days ago. At first, all seemed well. Chicks were lively, eating and drinking normally and running around the brooder. No one was huddling in front of the heat lamp nor huddling away. 2 days after purchase, I noticed one chick acting lethargic, hanging by the edge of the brooder, somewhat close to the lamp, not running around when I opened the brooder like the rest of the chicks. I immediately moved it to a sick brooder which is slightly warmer and got the "Save a Chick" probiotic. Within an hour of seperating this chick, it became unable to stand without falling to one side, arching its head back almost to its tail and falling over. It chirps loudly and keeps its eyes closed most of the time but will open one eye when handled. I have been keeping it warmer, feeding it the save a chick solution through a dropper, and keeping her calm allowing her to rest. Its been 24 hours since I noticed the first symptoms. None of the other babies have shown any decline (no loud chirping, they eat, drink, poop and run around). The sick chick has not pooped since being in the sick brooder but hasnt eaten either. No pasty butt. When offered water she barely opens her beak to accept and can be heard making a rattling sound when trying to drink and sometimes when sleeping. We've been practicing good biosecurity (take care of grown hens outside first, then wash, then care for healthy chicks, wash and care for sick) so I am hoping we can limit the spread. Is there anything else I should be doing for this sick baby? Any idea if this is an illness or simply failure to thrive? Any advice or opinion is appreciated.