This is Clawin
Its from too much N
A few ways it can happen
Too much N (feed)
Ph issues and N been taken up in excess
Poor feeding schedule
Feed Water, water (enzymes, calmag or low EC Nutrients to help break up core Feed) feed Water soil 1-2 feeds every 7-10days
Coco: feed water feed Water. Feed early then follow up water feed, or feed 1 day water the next
But its N