Do you notice the chicks standing in one spot, head withdrawn into their shoulders, and feathers all puffed out? If so, that's Coccidiosis for sure.
I think that when a chicken acts like that, it's more of a sign that something's wrong, not necessarily a sign of Coccidiosis. A couple of mine acted that way when I had a mite issue.
But having said that, I just had my first issue with what I "think" was Coccidiosis. I have all of my chicks on PenPal medicated 18% chick starter/grower and have been happy with it other than the fact I'm seeing quite a few of my chicks trying to eat feathers. I found out that the company has taken out all of the animal protein from the feed and I thought they may be lacking something in their diet. I personally think chickens need some source of meat. I had also heard that corn could be a contributing factor with purple showing up in black birds...not that it causes it, but that it might be bringing the color out more noticeably. After checking with the companies of different poultry feed, I found that most chick feed and layer feed all have 40-50% corn in them so I decided to go back to mixing my own feed and lowering the corn amount.
3-4 days after I had them totally switched over (I spent a few days mixing in the other feed to get them used to it) I noticed a couple of small tbs sized puddles of fresh blood in one of my pens that had 4 two month-old chicks in it. I thought it was an injury, but after looking them all over, I noticed a little blood around two of the chicks vent feathers. None were acting sick so I wasn't sure what was going on. I grabbed up those two and put them in quarantine, then ran back to the house to google what could be the problem. My coops are very clean and dry so the thought of Coccidiosis didn't seem logical. After much reading and a long conversation with the PenPal nutritionist, he explained that you don't "have" to have wet and damp conditions to get it and he thought that it was indeed Coccidiosis if I couldn't find any injuries. The amount of fresh blood had him a little concerned and baffled though.
I read that Corid was the best medication to use, so I set out to find that and eventually had to drive 20 miles because every place around here was out of it. I read that you don't usually see blood until day 3, the worst days are days 5-6 and by day 8 they are usually on their way to recovery or dead. I started medicating those two on day 4 and was still seeing a lot of blood. By this time they were acting very sluggish and weak and passing a lot of fresh blood. They wouldn't eat and was barely drinking. I remembered having 3 puppies (years ago) that had Parvo, and I was told that dehydration is the real killer so I treated the birds like I did those puppies. I got a syringe full of the medicated water and my son and I dripped it into each of their mouths 5-6 times a day to keep them hydrated until the medicine could have a chance to work. A third bird from that same pen started acting the same way with blood and one chick from a different pen (although that one wasn't bleeding, just acted slow) so I decided to medicate them all. One of the original chicks was so week and boney it could barely walk. I also dripped in some watered down Nutri-cal for some kind of nutrition. In addition, I also decided to dust them with Sevin just to make sure no mites could contribute to the problem.
Long story short, keeping them all hydrated worked, and all made it and are doing fine and pretty much back to normal. I added a tsp of Caro syrup to their water for one day, just to add a little sugar to their diet for energy and treated them all with a little yogurt for a couple of days and just bought some probiotics to add to everyone's water.
The real weird thing is, all 4 of the ones that acted sick were all from the same hen and rooster (blue on blue,
BUT just in a specific color. Those 4 were splash, but the blacks and blues from that same combo (and same age) didn't seem affected. Go figure!