If you aren't yet in flower, you can use a toxin. Look for anything labelled a "miticide". These are not just general insect killers but are specific for spider mites and other aphids. You need to attack the spider mites ASAP and full force. I discovered mine when my plants were already well into flowering. I tried insecticidal soap (non-toxic) but that only keeps them at bay. I have read where expert growers will recommend to destroy the infected plant and just hope the mites haven't spread to the other plants. These are VERY HARD to destroy and usually requires multiple applications and very close monitoring to see if they return. A sterile grow room is imperative too, as they could be anywhere on the floor or walls. Take this very seriously if you want to harvest anything worthwhile. Good luck.