that is pretty freaky. its in flower, when did you switch to bloom nutes?
it looks like you might be getting a little wind burn, the edges of the leaves are curling up a little.
the coloring does look like iron, but i've never seen anything make them fade from the central vein out before.
could also be sulfur, but again, thats a weird pattern
your light might be a little close, but if it was close enough to cause fading like that, the plant would already be crispy.
i dunno, if it don't get any worse, ignore it.