Stains, spots or?

One spot on one leaf...............is there really an issue? Don't worry.

Slightly serrated margin edges, more water going out than up the xylem, leaf tips show osmotic stress, which can be high salinity (ec) or wet/dry cycle drybacks are too much, causing concentration spike. Not necessarily too much but possibly plant is running out of water mid day or near end. I see some denaturing too which is indicative of short term overheating when leaves are very small and forming. The color of green across the plant is a little lime for my liking which means nitrogen may be affected in some way, too hard to pin point with so many possible variables.... Soggy medium and iron. Dont play well. My question time for the day is up, good luck.