I have a total of 5 chicks - my first 3 (Red Sex Link, California White, and RIR) that are now 2 weeks old, and 2 (barred rocks) that are 3 weeks old. I got the first 3 as day olds and the barred rocks were introduced to the others last week, when the BR's were 2 weeks old. I didn't realize until we got home that the two barred rocks were very different sized. One, as expected, was bigger than my younger chicks, while the other was about the same sized, if not a little smaller. The smaller one doesn't seem to be growing, although her feathers are continuing to come in. The other younger chicks have passed her in size. She's probably 1/3 of the size of the other barred rock, and a little more than half the size of the others. Her wing feathers look so awkward because they extend back further than her body since her body growth doesn't seem to be keeping up. She does eat and drink, however not as aggressively as the others. While the other 4 will crowd around the feeder and peck away, she might walk up to it, look at it, and then start pecking food off the ground in the litter around the feeder. She seems to lose interest in the food quicker than others, and generally will try to forage for it in the litter rather than eat directly out of the feeder (although once in a while she does use the feeder). Although she doesn't seem to be lethargic, she does just seem to be on a different page than the others, if that makes sense. She also is a noisy little thing, pretty much constantly cheeping. I've been separating her once a day to feed her some boiled egg, oats, and plain yogurt once a day to bulk her up. I separate her because if I add treats like this to the brooder the others flock to it and push her out of the way and she'll just hang behind to wait until the chaos subsides. I also add some vitamin water (vi-tal) to the brooder every couple days to help fill in any nutritional gaps. Since I've started this, I'm not sure i'm seeing any results. Any thoughts on what could cause this? I read somewhere that this could be a sign of cocci? She isn't showing any other symptoms, as far as i can tell. No signs of worms either (i don't know if that would be a problem this young). They are on organic starter, but i do have Corid on hand, would it make sense to treat her, or all of them?