Marc,

Just checked pictures in Cervantes' Indoor Marijuana Hortculture which I found in Boston over the weekend.

Has a picture of similar yellow spotting on the page for Magnesium (Mg) deficiencies.

Suggested treatments in the book - are:

Watering with a solution of 2 teaspoons of Epsom Salts to a gal of water.
"----or--- apply Magnesium Sulfate Monnohydrate".

----or---- Dolomite Lime at planting time.

----and--- then just stuff about temps. Root zone 70-75d F.
Ambient day temp 75d F
Ambient night temp 65d F

Would deff wait and see if Harddon and Zandor agree with the Epsom salts thing tho. Hopefully one of them can say this isn't the same kind of salting that locks up nutes.