Omg. Im sry for the non-detailed question. I left urgently to go look for perlite. Couldnt find any, but found gravel and river rocks in an aquarium shop. Only thing i can find right now... Can i use gravel?

The plants are aprox 20-25cmts from the 250w HPS bulb. Some are even closer than her and only she has this problem.

OMG!!!!!!!!!!!! UPDATE: i believe i found the answer. She was NEXT to the ballaster which gets REALLY HOT and maybe it was heat stress. I moved the ballaster. Il keep you guys updated if this changes her health