i water about every 2-3 days i fert every time but just a drop or two of vf-11 but i think joecal1 might be right i left out of town and the person watchin it didnt do his job the top touched the light and burned. however this leaf was at a lower spot and i doubt it touched the light
Light or nutrient burn nothing to worry about just carry on if the light is close then higher it a tad but only a tad.If the light are ok and it feels fine when you put you hand on the top leaves then it will be from a spill of nutrients when watering.