Mine did that only at the very very tips when I hit them with 1400 ppm fox farms last week. Not sure if that was the reason but like I said only the very tips. Yours looks like the whole leaf. Are they growing slow or seem stunned? Make sure your ph is good going in and out, my houseplants started looking jacked up and it was my ph. Also, I am totally new to this, these other guys know their stuff.