First grow mephisto genetic Double grape

Are ur leaves thick? They look so. Its neither from what I'm seem its overwatering. Or roots finding it hard to breathe from the bottom.. With the dose ur giving. Nute burn is unlikely. I don't see it. But I often see tat when roots are struggling to breathe. Either from heavy substrate, (tightly packaged) or u need to let the top soil dry in more as when it does air is drawn into ur sub and therefore helping ur roots breathe. Nute burn id see more crispy tips.