nspidermites are hard to kill.
neem oil seems to do the trick.
doesn't kill them, those fuckers don't live past 30-something hours. it prevents their eggs from developing properly. the problem is that most pesticides kills the live ones, but the eggs are covered in a protective goo that makes them keep coming back in bigger and bigger numbers.
it's gonna be a battle. get ready.
here's one of the links. google neem oil roll it up and you'll find plenty of sources for this:
https://www.rollitup.org/general-marijuana-growing/8962-how-use-neem-oil-without.html
if you've seen the buggers in the SOIL, then spread about 1-2 inches of sterile, clean sand over the soil. it's readily available at home depot and such, for children's sandboxes. that will suffocate those little buggers, without having any adverse effects on your plants.
you don't have to order it online. they have it at walmart, walgreens etc. etc. it's not hard to find.