Whats wrong with my leaf?

I am growing blueberry in super soil, they are 3 weeks into 12/12, and out of a whole tent, this is my one problem leaf. Any ideas whats wrong with it?

maybe its just a local burn of some sort. a splash?

I was thinking it might be a disease. Its at the middle of the plant, far away from the watering hose. I am just giving them RO (with silica to 50ppm) with compost teas every 2 weeks.

Could my tea burn the leaves like synthetic fertilizer if i did manage to get some on this one leaf?