My black cat seems to have dandruff?

I have been brushing him and his mom and brother (they are Tabby's and i don't see it on them or the fur when i brush them) I was wondering if anyone had advice. He doesn't eat people food, just purina one mainly. i have not seen him itching or any excessive grooming... does anyone know any over the counter treatments? like everyone in this economy the less money the better, but if this is an indicator of something that needs Professional treatment we will head to the vet.