I am a newbie to raising chickens. History: I have BO chicks now 11 wks old I've had since a few days old. On medicated feed from the start. Lost one chick at 3 wks & went on BYC & consensus was coccidia. First treatment was with Sulmet because it was all I could find at the time. A week after the sulmet treatment, I found Corid & treated with that 1.5 tsp/ gallon water for 7 days. I lost another chick around 5-6 weeks & consensus was to treat with Corid again. Same dose & duration. I had another chick get sick & I did a 3rd round. I have never seen blood in the stool of any of the chicks up until yesterday. I keep trays under the roost. Yesterday I saw 1 stool with mucous & red area like blood. Today there was even more. If I am seeing blood, it can't be good. I don't see roundworms or tapeworms & like I said they are only 11 wks old. I am starting Corid again but maybe I have treated too often??? What else can cause blood in the stool? I also had mites in the coop & treated chicks with permethrin poultry dust & the coop with liquid permethrin & repeated 5 days later. I retreated today because I saw a mite in their poop tray. Also about a weak ago I isolated one on the chicks for what seems respiratory, wet sounding breath sounds & she was listless. There is no visible blood in her stools & she is still away from the others. The well chicks (3) show no signs of respiratory issues are active, eating & drinking, have pink beaks, don't seem anemic. I don't know if the blood in stool is just from one chick or all 3. Most of the poop except 1 -2 droppings look OK. I just recently had a small yard tractor made for them & have let them out in the grassy area the past week or so. There are a lot of weeds, could any weeds cause this? I am adding pictures. Thanks in advance for any advance. Please, even though I know people mean well, I am not ready to cull these chicks yet, I want to give them a chance.