Is it organic and are you feeding the microbes. Or giving any teas? I’d say your problem is the nutrients are In a form that’s locked up and your soil is not alive enough to make them available to the plant.

Also I’m gonna tell you it’s getting plenty of light, when a weed plant is put into a low light situation what it does to compensate is darken its leafs to a forest green color as to better absorb light I have a whole mother plant room that has all the leds turned/ dimmed down to the lowest setting.