For scaly leg mites (you should be able to see lifting of the scales on the legs if that is what it is) you need to treat for 2 weeks because of the life cycle of the mites, and what I have done is to dip the legs daily in mineral oil (veg oil would work) to smother the mites. They will die - bag balm didn't work for me as well as oil but then I have only treated it 3 times and maybe it was a harder case to treat or something.
Ivermectin pour on also is effective but technically you I believe need a vet to prescribe it when used as an insecticide (it is available without prescription).
Scaly leg mites also occasionally attack the face, so you can smear some oil over the comb and wattles if necessary. This will work its way through the flock if you allow the bird to roost with the others before the bugs are killed. I allowed my 3 birds (one at a time - was the case) that I have treated in the past- to flock with the others and roost with them, taking the chance and since I treated it daily I was fortunate and it didn't spread through the flock. But I also was dusting the coop and spraying things.
Best to be safe and quarantine if possible. A month long quarantine is recommended anyway with a new chicken- even then there are diseases where they are asymptomatic carriers and can pass quarantine.
He is a handsome boy!