4 weeks, hunched, tail down, and now limping , day 4

[freefly]

I have two chicks 4 weeks old.
They are raised free range with there mother hen.
I feed them medicated starter chick feed.
4 days ago one of them seamed hunched and not keeping up with the others.
He was better on day 2 , 3 and today day 4, but now he is limping and still hunched with it tail down.
Eats and drinks ok.

I don't see blood in his stool but there is a redish or brownish color to it.

Any ideas

 

[asher]

My first thought is coccy for sure, even before you mentioned the stool color. (I've had birds before that I KNEW had it, without seeing blood in their stools.)