also, you don't HAVE to medicate at all. i raise all my birds naturally- no vaccines, no preventative medications (including medicated feed), and only treat with medication if it's completely necessary. only once have i had a chick die, and i'm pretty certain it wasn't from cocci. i use the deep litter method to slowly build up the chicks tolerance to cocci- they are going to be exposed to it regardless of what you do, and as long as it's a gradual build up, then their systems can handle it.
what i do is stir the litter every other day to keep it from getting really messy. i throw a handful or two of fresh litter in the mix at that time. then, every 5-6 days, i add about another 2 inches of litter on top of what was already there. i continue this the whole time they are in the brooder. my brooder is a big watering tub (3 ft deep), so it can take a lot of litter, but you may have to clean yours and start over at some point if it's more shallow.
also, introduce your chicks to the outside world slowly- take them out for an hr to start and build up. you can also bring a little bit of grass into them when they are 2-3 weeks old. slow introduction to the parasite builds up a natural tolerance of the parasite. also, giving them live culture, plain yogurt (i'd say about a tablespoon/ chick every 3-4 days- try putting some Cheerios in it if they won't eat it plain) will help keep their digestive systems healthy, which will decrease the likelihood of the parasites becoming a problem. greek yogurt is a really good option.
here's a good place to read about
holistic, natural prevention and treatment of cocci.
don't let this setback stop you from keeping chickens. all of us have received bad advice at one time or another. but, you're in the right place now!