Could be a fungal problem or a big calcium/magnesium deficiency, or even both.
To be honest, I don't think you grasped the concept of "close up" and "big bang yellowing" is not a diary, just a couple of pictures.
Sorry, but can't really help you so far.
What are you feeding?
What are the grow conditions?
What is it growing in? Soil? Coco?
Three or four clear, close up pictures would be helpful.
Details, we need details!
Please.
Thank you.