Aloha brother,
If your pH is good and the plant is getting all of the micro nutrients it needs, then i would say it looks like some sort of disease/mildew/mold. It is possible it is from a pest but more likely the humidity is bad for that strain. Do you get vog there? that is similar to what other plants show when damaged by vog.
If you believe it is a vog problem then washing the plant off will help. If it is a mildew problem then watering the leaves would be bad.
I would isolate that plant from the other undamaged ones, so the disease cannot spread - mold spreads thru spores
do you have dramatic temperature differences from day and night?
good luck and please document everything you notice, from where it begins, coloration of leaf/veins/stems, curling up/down, new/old growth etc