what could this be?

If you are still using the 1000w I'd have that dimmed to the min and at the top of tent. Too powerful for veg I think

Not much wrong with them pal. Though limited info. Just to look at them they look quite short. What I mean is the distance between nodes looks small. I suspect maybe your light is too close. The curling over if that's what I see indicate similar.

They look ok to me ,but why would you mix soil and coco ?? Together ,I use biobizz light mix and for me it’s a good soil without putting extra coco in it ,I just adding more perlite .

lower your pH to 6.2 What I see is some environmental issue. You didn't mention your temps and humidity average, what are they? You can reply to your question with the added info. You wanna shoot for a mid 70's temperature with a higher side humidity in veg. Like 65 to 70% RH You also need to move the air around in your space if you don't have some sort of oscillating fan.