Safer Insecticidal soap, twice a week for three weeks. Kill the living before they get old enough to lay eggs, then kill the hatchlings, again before they get old enough to lay eggs. Repeat this process for several weeks and they'll be gone for good.
All the crazy talk about bleaching the walls, etc is totally unnecessary; they only live on plants, so concentrate your attention there.
Finally, they came from somewhere- could have been you coming from a buddy's house who's also infested, could be a friend, could be your dog- seriously. If you've been someplace where there are spidermites, change clothes before getting anywhere near your ladies. Do NOT let pets around your plants, ever, this is just one of many good reasons. This is the best reason to limit traffic around your grow.
You found them early so damage is minimal.
Be sure to spray both tops and undersides of all the leaves and stems- they live on the undersides of the leaf, not on top.