That's a good sign! If the area or brooder is dirty or wet, keeping it clean will help with the parasite load the chicks are ingesting as well. Making sure the chicks are well fed, watered and comfortable to reduce any stress on them will help as well until you're able to treat them.
My chicks were in a dry kennel on clean dry paper when the blood appeared in one's droppings. The chicks never looked sick, but they had appeared more tired than usual for 2-3 days prior to at that first bloody stool. They responded well to treatment.