Could you show us some pictures...? Of the droppings, the chickens, and,
why not, the coop...?
...Could be anything and everything...
First : Did you deworn your chickens?
I would try to help them by mixing some
food grade Diatomaceous Earth to their food, in a (plastic) feeder...
(I would be careful to not give them a dewormer that could weaken them...)
I would also put some
Apple Cider Vinegar (1 tablespoon by liter of water) in their (plastic) waterer...
Second : Did you weigh your chickens?
Do you think they have lost weight...?
...Just to be sure, I would treat them against lice/mites. Again, personally, I would use
food grade Diatomaceous Earth : that works miracles. (I speak from experiences, but I
know others think the opposite...?)
Third : What do you feed your chickens, exactly?
Sorry : my Internet is bad, because I'm in the countryside... so, I
can't load the page you have shared, and I am not familiar with "
Tractor Supply".
...Do your chickens have access to layer pellets? I would recommend you give them some, but I would first like to know
what you are feeding them...?
And do they have an unrestricted access to their feed all the time?
Fourth : Do your chickens freerange?
Can your chickens eat grass...?
Do they have access to some toxic plants?
Do they have sufficiently space...?
...Give details, please. Even if you think they are not important, because they
could be...