well, with only one like that, it looks sort of like when i sprayed mine and the light burned where the water drops were. no idea about anything, but just saying it looks like that to me, and i would think if it is some deficiency it would be on more leaves than one... but i know nothing and have just started my first grow... another hint for me to say that is that on mine, the leaves curled up a tad on the very edges and that turned out to be the light too close and not dimmed enough for their age and place. but once again, i know nothing, just relating my one experience... id listen to the farmers here, they tend to know their stuff!