It's a Cal-MG deficiency. Are you using R/O water? If so add a tablespoon of Epson Salt to every gallon of nutrient mix. The quickest way to fix is make a liter with one teaspoon of epsom salt and foliar feed the girls that way if it fixes the problem I would add to nutrient solution then. What nutes are you using? You also may want to buy a Cal-MG supplement if you are using R/O water.
