Are you sure that they are spider mites? I would begin by spraying with a very light mixture of organicide or neem oil. Or dunking the whole plant in a bucket of water and neem oil and holding it there for about a minute. To do this take a piece of cardboard and cut a slit from the center to the outer edge which you can use to collar the plant at the pot so that soil does not fall out when you tip the pot upside down.