Hi there. I understand your concern and you obviously have the best of intentions for your little guy.
If he is not a fresh chick it is best not to administer medicated feed...especially if you suspect he is already sick. This is strictly intended for early stages of a healthy chicks life to encourage immunity. It is not going to help him if he is sick and can in fact be counter productive.
If you have researched and suspect coccidia and have a vet available they can diagnose and give you antibiotics to treat your flock. You have done the right thing to separate him and give electrolytes.
I would continue to monitor him closely and if a vet is not an option there are several home treatments you can start to work on. He needs nutrition, his immunity boosted, warmth, and to have the coccidia challenged...if this is what you believe he has. Medicated water, palatable nutrient dense food such as corn meal porridge, oatmeal, meal worm, fish, vitamin water. Fresh garlic and broad spectrum probiotics are effective tools. He will need to eat frequently. Heat lamp. Frequently changed bedding.
Chaga tea to challenge the coccidia and increase appetite, reduce inflammation, protect his delicate guts, and induce a system wide anti viral environment.
These are the protocols I follow.
I also use apple cider vinegar with the mother.
Boost immunity any way you have available. If you are feeding grains start fermenting them to maximize nutritional availability.
Others will also be along with their great advice.
Stay calm. He will benefit from your peace and love. And of course, say your prayers.
