Athosanswered grow question 7 years ago I'm going to go on a different route regarding your symptoms. I see purple to blackish dead splotches on lower leaves, severely affected leaves with metallic purple color contorting and withering, those are textbook symptoms of phosphorous deficiency. Since you don't mention it I assume you are not measuring nor adjusting pH.
I believe you might have deficiency due (a) pH been in the wrong range, or (b) after 6 weeks of veg growth that 1 gallon of soil is somewhat exhausted of nutrients, so either pot up to bigger pot or start feeding.