Does Anyone Recognize This?

[Shawn MT]

I've looked at several charts and can't identify my issue. Magnesium, calcium or boron deficiency or just leaves dieng naturally. It's only on the bottom leaves and only on one of three plants.

 

[fatawa]

Hard to tell with blurple light.try getting one n natural light.how tall are yur plants?cause they dnt naturaly loose leaves at a young age,usually only wen older and light isnt peneratrating bottom branches.do you use a cal mag supplement?and what r yur feeding schedules/amounts(ppm/ec)?