Yes, mites are visable with the naked eye, and yes, it they will destroy your crops in no time.

Either get some neem oil, and mix 2/3 water, and 1/3 neem oil, and spray your plants lightly. You can also use non-biodegradable dish soap too, but it has to be non-biodegradable. Again, mix 2/3 water, 1/3 dish soap and very lightly mist your plants.

As for legal buds, why bother.