Hi. I'm about 3 weeks into flower (growing Black Cherry Punch in DWC) and most of the fan leaves in the upper canopy yellowed over a 48 hour period

At first I thought it was light burn but now I'm wondering if it's nutrient burn

I raised the light and flushed the tank (ppm was 2500). Is there anything else I can do? Will the buds adjacent to the damaged leaves still develop? Thanks