It is difficult to get off... it has been on some leaves of the plant for a long time. Since... about halfway through veg. I do not have mites. I recently had a small bug worm attack that killed two of my baby clones and tried to get at my other plant but thankfully it only took one top. I still havent found one on this plant, which is a bigger reason why I am stumped as to why it has leaf abnormalities.