This is the start of an Overfeed. I think thats more an orange colour lol but the postion its in on the leaf is definatly an overfeed im a dwc grower so its something im pretty familiar with when shes dry give her normal ph balanced water for a week then reintroduce the feed at a slight lower ec or ppm value and you should be alright :) Best of luck for the rest of the run :) 👊