Sorry the pic is really fuzzy but the caption says 'how am I supposed to water this thing?'

It's an asshole plant.

Anyway I would guess a couple things... those patches COULD be an advanced Mg def, but they are kind of irtregular, so hm..

MY first place to start would be that your soil wasn't really that well mixed and you've got a 'hot spot' of crap pH. A good thorough flushing is a good place to start, and check your runoff. The curled-under leaves too would indicated that it's time for a flush anyway.

The fact that you see the spotting only on older leaves is good. It may just be scars from damage from a problem that no longer exists (flush anyway just in case!).