I had a two year battle with mites that came from my clone buddy's place. Some plants out in the greenhouse were going to get tossed and I knew there was bugs on them but in my arrogance figured I could deal with it. None of the plants survived but the mites sure did.
My problem was not being consistent with my spraying but finally got my act together and got rid of them.
I used Safer's End All concentrate mixed up as directed but added 10ml/L canola oil to suffocate the bastards. One 500ml bottle cost the same as 1L of the pre-mixed spray but makes 10L. Made sure to spray really good with a strong light behind me to be able to see any missed spots and did it every 4 days for 4 treatments. Never seen a mite since and that was a year ago. For the grow room I just kept it warm and no plants in there for a month so any bugs would starve to death and any eggs that hatched those mites would find nothing to eat and starve too. Didn't do any sterilization or anything else. If allowed to cool down the mites go into hibernation and will wake up once warm. The go red when ready to hibernate too so I kept it at 80F as the warmer it is the faster their metabolism and life cycle is.
You definitely want to be checking for bugs all the time. That one leaf with a few spots can turn into a war in a week indoors and if in flowering it's no picnic fighting them by hand like I did with a thrip infestation a couple years ago. We only seem to get thrips and mites here since I started filtering my air to keep the fungus gnats out.