Approx. 2-3 week old chicks (4 Barred Rock Plymouths) with blood in stool; lining or coccidiosis?

[fowlplay_suspected]

Title says it all. Last night I discovered some red in their droppings. And today, they have had a bit runny stool and the red is still there (even if it's only a little). I can't imagine how they would have gotten coccidiosis if that's what it is, since I've been practicing good biosecurity, but I know that with parasites, when there's a will, there's a way. Should I begin giving them medicated feed and dosing with Corid? What would the dosage be for chicks so young? They're 3 weeks old (if that).

What would the after care be once I dose them with Corid? I didn't have to do this with my first batch, so I haven't had to worry about that yet.

They are as alert as ever, divebombing eachother and squeaking and huddling to me to feed them or tidbit with my nail on my hardwood floor. I have been feeding them Dumor starter and they have constant access to fresh clean water.

Poop pics attached. If you don't wanna see that or are eating, maybe avert your gaze. Lol. Also, the ones on the paper towels I had to clean off the floor, so that's why they look weird shaped. Such messy little ones.

 

[ChickenCanoe]

Stick with the Corid only. Coupling that with medicated feed could overdose them.
What is the bedding in the brooder?
Coccidia can come from equipment that has been used outside or from your shoes.

 

[fowlplay_suspected]

Stick with the Corid only. Coupling that with medicated feed could overdose them.
What is the bedding in the brooder?
Coccidia can come from equipment that has been used outside or from your shoes.

The bedding is just a few puppy pee pads. Bah, so sorry. That detail slipped my mind. Those have not been used outside. Genuinely cannot understand how they may have contracted it if they have. What would the dose be for them?