SERIOUS UNKNOWN PROBLEM, please help!

My plants have been doing fine for the month of their lives, but recently they have developed yellow blotchy patches, curling upwards and becoming crispy.

I have no idea why they are doing this.
I thought i was magnesium def, so i added Epsom salts. And it couldn't be nutrient burn as they were doing fine the whole time.

they only started to decline after i moved them out of a shaded greenhouse to next to a fence and a metal shed

Could it be a mixture of over watering, and too much sunlight? possibly pH?

please tell me your thoughts!
 
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