Let me start by saying that I live in Panana, it's hot and humid here, year round, both day and night. It rains every day, at least for a couple hours (usually in the late afternoon) for eight months of the year, and is bone dry the rest of the year. The ground seems overwhelmed with coccidia, and before I started them on Corid the same day their 'boots hit the ground', I was losing half of the hatch, or thereabouts. Sadly, once I discover that a baby chick is sick with this opportunistic parasite, it's usually too late to reverse the damage caused. So...
I've since transitioned into using non-medicated feed (21% protein) so that I can feed it to my entire flock, not just chicks; this is the absolute best feed that as available for any bird in this country, and it's only carried by one feed store; the rest offer 7% protein as their top-of-the-line poultry feed. I don't worry about the loss of vitamins as I add ChickBooster (TM) to their water every day (except for the week they're on CORID), even the full grown chickens get ChickBooster. I buy this in the largest bottle they sell, 1 liter, and I buy several bottles at a time because once they run out, it's unlikely that they'll have more for a year or so. Don't ask me why, I don't know why... It's just how it is here. I stock up on Corid the same way (expiration date kept in mind, of course), as it's another item that once they sell it all, there's no telling when they'll get more (or even if it will be in-date). I've had need of Corid in the past where EVERY feed store in the city I live in, arguably the second-largest in the country, had none and didn't know when they would get more. I lost all but a couple of birds that hatch.
So, now that I've written a book about the subject... The reason WHY I do it this way instead, is because this way worked for me and my flock better. Different locations, different solutions. Please note, I'm not saying that you're wrong, just saying that it didn't work well for me.