Poop alone can't give you definitive information about the presence of parasites. It can, as this poop does, give you a reason to have it tested for parasites. Any vet, with adequate persuasion can run a fecal float test for you on poop samples. Just assure your vet you will assume the responsibility of treatment.
That poop may be negative for coccidia now that you've used a coccidiostat on the flock, but if worms are present, it will tell you and also what kind they are so you know what worming med is best.