The yellowing started from the bottom the nutrient are terra flores 50ml per 10ltr with the additives
From the bottom up is possibly N and/or MG, were you using terra vega before flipping the lights?
If so, did you continue using it for the first 2 weeks of flower?
If not, its easy to go overboard with P&K too soon which can slow the uptake of iron/zinc/magnesium and it will show on the hardest working plant first, high CA tap water can cause similar/same issues.
Are your other plants starting to show similar symptoms?
From what it seems like, you cut N too soon and started to high of a P&K feed too soon, that's why its good to put the history up, it really helps get to the bottom of things. What you've fed in veg,room temps room rh ect ect.
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