That looks like coccidiosis. Are any looking lethargic or puffed up? How old are your chicks? I would get some Corid, Ampromed, or Amprollium liquid or powder from the cattle section of your feed store, and start it. Dose is 2 tsp liquid or 1.5 tsp powder in 1 gallon of water. Treat all chicks for 5 days, and if any are still sick, 7 days. Give vitamins and probiotics after completion of treatment. Then you may want to repeat Corid in 3 weeks with 1/3 of the dosage in the water for another 5 days just for prevention. Here is some info: http://www.the-chicken-chick.com/2012/12/coccidiosis-what-backyard-chicken.html
Oh no! I have 3 that are 6 1/2 weeks old and I have 2 that are four weeks. The 2 brooders are separated by netting so they can see eachother and I take all five out together for socialization. I didn't notice any of that color poop since that one time this morning. All are eating great and drinking fine. And they are on medicated food. I have not had the best of luck so far. The second batch of chicks who are now 4 weeks I lost two. The one silkie I brought home cried and cried and passed away within 3 days. Then my silver laced died at 3 weeks from an impacted crop. But now I'm wondering if it was cocci? This has been so frustrating and I thought I bought the girls from a reputable breeder. I don't want to loose another one! Wouldn't they be pooping that color more often if they were infected?
You can watch them for signs of becoming sick. Watch for more orange to red poops. They can normally pass a little intestinal shed now and then. Any lethargy or puffing up, and I would treat them. Get the Corid and keep it on the shelf just in case.