Light burn vs heat stress — how to tell the difference?

Had this exact issue last grow. What fixed it for me was flushing with pH'd water and letting the soil dry out before feeding again at half strength.

Looks like a classic case. Check your pH first — 90% of these issues trace back to pH being off. Even small deviations can lock out nutrients.

Environment is key here. What's your temp and humidity? Sometimes the symptom looks like a nutrient issue but it's actually environmental.

Post a picture if you can — hard to diagnose without seeing the actual damage pattern. But from your description, I'd guess pH-related lockout.