I'm no expert but I don't think you have spider mites. Are any webs or webbing between leaves present? It looks more like a fungal issue to me. Look on the under sides of your leaves with a microscope or a magnifying glass and see if there are any bugs. If your worried get yourself some organicide. You can get it at Home Depot and it works for mites, soft bodied insects, and fungus and mold. Good Luck Dude.