Do you know the temperatures inside your grow room?

Hmmm... I know my plants had two or three leaves like that, but I never really took much notice, as the affected leaves where less than 10% of the plant.

But, in your case, just to make sure, I'd re-mix the nutrient mix, and make it 50% strength. Upgrade it gradually....

But again, I don't know if your problems are because of nutrient burn.

Best,

-turtle420
.