I live in Aust
I live in Australia. I do not know what a "feed store" is. I got the chicks from a random guy, not sure if he was registered. I'm pretty sure they were vaccinated, he did say. If you can tell me where to get chick grit i will, but I can literally ONLY FIND CALCIUM/SHELLGRIT AHHHAre you for sure they were vaccinated for Coccidiosis?
Even in the US, that is not a widespread practice except for large commercial operations.
The Coccidiostat in your feed is Bovatec® 20CC (Lasaloacid Sodium) just in case you need to know that. If the feed store guy recommended it, then I would stick with that for at least 6 weeks or so.
Please do provide the chicks with a source of grit - if they eat anything else besides chick starter they need grit. This may be why you are seeing some "off" poop.