Red mange keeps coming back

I taper him off the ivomec slowly. I never hunt him while he is being treated. He seems to start feeling bad with the start of hair loss. I never thought about a weekly dose and no I have not talked to my vet about getting him neuterd. I don't think the ivomec make him feel bad, he seems to start slowing down and not very playful when I notice he is loosing hair. I keep a very clean kennel, fresh water every day and he eats good all the time. I have been feeding victor 24/20 for a while now. I have 11 dogs and everyone else has a slick shiny coat. I just don't know what to try next!