could u recommend somethinglooks like a zinc dificiency, flush the plant with a diluted nute mix contaning zinc, iron and manganese elements.
also calibrate your PH meter as this could have caused your problem.
DTM
ZINC (Zn)
White areas form at leaf tips and between veins. Occurs in alkaline soils. Zn deficiency can be treated by burying galvanized nails in the soil. Chemical fertilizer containing Zn can also be used.
what are you growing in? i would flush the growing medium as long as it is not a bag of miricle grow or anything similar, keep us posted on your progress!oh really damn ok pure water for a week then just to see how its gonna turn out