How to help my dogs dry skin?

I have a chihuahua and he's got really bad skin recently. I've been brushing him everyday for a few days not and there is a lot of dandruff falling off of him and he's shedding like crazy. I bought Nourishing Naturals from a local pet store and it's leave in conditioner to keep their coat hydrated. But it isn't helping and I've been putting it on him for about a week now. Does anyone know a really good working spray for his coat I can use? I don't notice him itching too much but he just has a lot of dandruff and shedding like crazy. We don't give him baths a lot so it's not that we're drying out his skin.