Help and fast!

[GermanKennhuhn]

As previously mentioned, how far apart are they housed? Have you been going between coops with the same clothing and shoes?
The bloody droppings is likely coccidiosis. Can you buy Corid?(durvet-lamb-and-kid-omega-3-plus) Hope this link works.
Dosage for Corid is 2 tsp per gallon of water for a week. Replace water daily.

 

[GermanKennhuhn]

I haven't been changing clothes as I did not think there was an issue. Do I need to treat them all (existing flock and new ones) with corid?

I meant mainly for mites. I would treat them all for mites/lice just in case. The permethrin recommended in the previous posts is best.
If they haven’t been in the same coop, and no droppings got tracked into the existing flock’s run, there’s a chance they don’t have coccidiosis. It would hurt to treat in case though.