I’m gunna go with to much nitrogen even under those cheap purple lights those leaves r glowing. What r u feeding? What’s ur ph? What medium are u in?
looks like what @GorillaGherkin said to much nitrogen ,,you can see that the leaves are curled down an inwards,,mac.
Your leaves have "the claw" and are dark colored, just like everyone else said, Nitrogen toxicity. You can learn more about diagnosing plant issues at: www.growweedeasy.com
I flushed them with PhD water I figured it was a nitrogen problem from all the research..im using a mother earths groundswell soil...i realized later on probably isn't the best soul for a beginner..but ive seemed to keep them alive...at the beginning I used a fish fert with molasses and phd water..then I added cal mag and phd water.. And since ny lights are cheap could you recommend a good one!