Leaves going vaguely black at the top

Athenry04

Member
Hi, I'm a new grower and have been growing some autos. They have achieved a smal size due to me having a shitty set up at the start which I've now improved. The plants have been flowering for a few weeks but the leaves have recently started going from a dark green to a light green nearer the top. The lower leaves are starting to twist and turn yellow. However, most worrying is that some of the tiny top leaves near the buds are starting to blacken around the edges. I have no idea what is happening, any ideas?
The first two picks show the curling leaves, which seem to have got worse over night. And the third pick shows the blackening leaves at the top.
 

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