Light burn or Lockout??? Please help.

[BrettJA]

Growing in a 2x2 in fox farms ocean forest soil. Plants are reaching quite close to light. Feeding mega crop 1 part, as well as a lil bloom from GH. Watering at ph of 6.3. Symptoms are confined to only one leaf at this time.

 

[LoveGrowingIt]

It could be light burn. It's hard to set the light level when the plants are so tall. Supercropping might help.