I like this idea:
-- Spraying mites with neem/pyrethium - Blitzkrieg --
Take advantage of your light cycles. While your lights are on, they won't move... at all. They hate ultra violet light as it dehydrates them, they get a sort of heat stroke and die. So they will be out and about when your light is off. I like to wait until a few hours before my light goes on, as it's for sure that any mites that want to get around my plants. That's when I get them.
Nothing gets rid of mites like a good downpoor. They drown, get knocked off, and generally hold on for their dear lives. During my dark cycle, I'll spray all over the plants, and I mean really really spray. Dripping wet. Then I'll get underneith the leaves, where they live and hide, and spray the hell out of them. I do this with a progressive neem oil mix - two caps of oil and 2 squirts of soap in my spray bottle - the next spray cycle 3 caps, the next spray 4 caps, etc. The reason behind this is because mites build up a tolerance to neem quickly, and more will be needed each mixture to get those persistant mites. The reason why you want your plants dripping wet is because neem and pyrethium have a low residual action - it only kills what it comes in contact with.
The idea behind adding soap to your neem oil mixture is that the soap will create a film, such that it will choke off the tiny throats that the mites breathe through. As well, it allows neem oil to disperse through your water mixture (soap bonds with oil). The plant is not effected by the poison (be it neem or pyrethium), but rather by the soapy film. If you put too much on, it will kill plants. Why? This film does not allow the chloroplasts- the cells that do the work in the leaf - to exchange necessary gasses. So after about a half hour of application, wash that shit off your plants! Besides, any power the neem or pyrethium will have will do it in the first half hour - they have a low residual action, they will only kill what they come in contact with. So after you spray your solution on your plants, make sure to wash them off about a half hour later. Really really spray, once again, like a rain storm, possibly multiple times.
Spraying frequency is a big issue and needs exact timing. Over spraying your plants with neem oil will cause the mites to build up a tolerance, underspraying will allow the mites to re-lay their eggs, continuing their growth cycle. The idea is to time your spraying with the mites' hatching cycle - every 5 to 7 days. That first application will kill off those first round of mites, but the eggs will still be around to hatch 5-7 days later. So, be persistant in killing off the next generation, apply your neem/pyrethium every 5 to 7 days! Any more than that is a waste in my mind, and further builds the mite's tolerance.