well, the mottling is not spider/broad mites, although you can have those doing other things. So don't go all crazy poisoning your plants unnecessarily.
there is no definitive answer to what is causing those symptoms you are experiencing. some claim a deficiency, those people are usually trying to sell clones. I have seen this "deficiency" spread between clones so it does seem to be infectious.
If you have the liberty, you would probably be best off tossing all affected plants, but I know this is in some very cherished clones...
oh, my best guess is the Asters Yellows - google will show some scary pics!