Rust spots on leaves

I just noticed these spots this morning. It's only affecting two of the larger fan leaves on a single plant. Both of the leaves are somewhat older, so this *may* be left over damage from my pH nightmare two weeks ago.

Grow details - hydro drip feed DWC system. pH is at 5.6 and TDS is at 920ppm using the Lucas Formula (top off meathod). Lighting is provided by a single 42w cool white CFL over each plant plus a couple of 36w daylight CFL's on the side. Res temps are at about 75. Room temps are averaging 80 - down to 75 during lights off, as high as 83 during lights on. Plants have been on 12/12 for about 10 days now.

Any thoughts?

Get a shot of the underside?

Hmmm...Can't get more pics until tonight when the lights come back on.