Why?

Magnesium deficiency maybe. If you are growing in coco, you need to give cal/mag from virtually day one. But without a diary and/or a lot more information.............who knows what you are or are not doing.

It looks like it could be either a deficiency or a pest issue. Check the undersides of your leaves for white or black spots, as this could indicate pests like spider mites. Also, verify the pH level of your water; if it's too high, it could cause nutrient lockout. Be cautious about reusing soil unless you know how to properly amend it. This could also be a calcium or magnesium (CalMag) deficiency.

that's a weird drying pattern. whatever it is it'll be exacerbated by your watering habits. Always saturate entire volume of substrate - never a partial water. Allow top 1" to dry and repeat. If you don't follow these basic concepts you are watering wrong and adding to any problems you see. Could be a bit low on N. (paling from bottom-up on plant.) Chlorosis in new growth could be too much P or K or even an S deficiency. Could be that the light is a bit too intense. Leaf symptoms are not discrete. More information is needed. Might be related to poor watering habits.