That could be a couple things.
Suffocation... when your plant is in a badly-ventilated grow space you will start to see those 'canoe leaves'.
pH issue... is that PEAT I see in your soil? Looks peaty. Flush the crap out of it. Check your runoff. Adjust your pH if it needs it... and by the looks of things it REALLY needs it.
Good news is that you are not past the point of no return. That plant can be saved.