I am a mmj patient and my caregiver in the summer had some neighbors with spider mites, exhausting right at the garden.
She found these "Predator Mites" that you sprinkle over the plants.
She said it costs like $50 for a container the size of a film container. Accompanied with removing/vacuming off webs worked for her.
Also, for indoor I heard, if you keep your temp below 80f(unsure of specific temp) you won't get them in the first place.:thumbsup: