I had the grain mites infested my mealworm containers about 2 years ago. Ever since then, I put all my worm and beetle containers within a tray of detergent water hoping that'll keep out the mites. However, I just discovered 2 of my containers (out of 7) got infested again!!! Grrrr...!
The other time when my worm colonies got infested, there were tens of thousands of those dust-like creatures, throw in a piece of carrot and it'll completely covered with the mites in half an hour. This time, its slightly different; the mites seems spherical and much larger (~0.5mm size), there are not that many of them, I can only find dozens (maybe a hundred) of them each time on the vege; but that's enough for me to throw away the containers.
Don't know what else I can do keep them away.