Fungus, deficiency or burn?

Hi guys.

I'm currently growing a few plants from clone and yesterday I noticed some orange spotting on a few of the leaves about midway up on my Walker Kush. I'm hoping somebody might help me with a diagnosis.

Here's the current stats:

4 weeks veg in Roots Organic soil.

Fed with Fox Farms Grow Big at week 4, and 5. Maybe a bit heavy...

Gave half dose of Tiger Bloom 1 week before switching to 12/12.

600w MH for veg.
600w HPS for flower.

2'x4'x5' Apollo Horticulture tent.

24" box fan
6" 240CFM inline exhaust fan.

pH is close to neutral 6.7-7.2? Using the liquid so I'm estimating based on color.

Been using tap water.

After spending a few hours researching I think I've narrowed the problem down to three possibilities.

1) Rust fungus (PLEASE NO!!)
2) Calcium deficiency or toxicity
3) Nute burn

At 30X magnification I was unable to distinguish any spores so I'm hoping rust is off the list. I did some extra defoliating just in case.

I definitely don't want to make anything worse so I figured I'd ask here for opinions before my next step.

Any help is appreciated!

Thanks all.

when my plants look like that,i give a little cal-mag seems to workalso if that roots stuff u use is there coco in it,if so try to get ph down a bit.i like to run 5.8 -6.0 in coco.

Hey thanks, Thumper60. As far as I know there's no coco in the medium. I removed the affected leaves and haven't seen any new ones looking similar, so I'm hoping I dodged the bullet.