There was a great article in one of the recent magazines about using a powdered sugar shake to test for mites. You can determine if it's varroa or tracheal, though I suspect varroa. I'll try to find it. Once you determine that...
HopGuard? If you use it as prescribed this time of year, it won't solve the problem, but it will buy the colony some time. I say that because it will do an incredible job of knocking back the freerunning mites, but you'll still have a huge load inside the cells. You'll have to continue monitoring and/or combining the treatment with something else like Ray's grease patties or powdered sugar shakes.