What are your ideas?

Cuz I'm not sure and want your expert advise if you have some.

Anyone? BUMP

Looks like a water burn. Is that the only spot?

Looks like a water spot burn, did you foliar feed the plants recently? If so, you want to keep it at a very fine mist, almost atomized. Whenever I foliar feed I do it when the lights are off or I raise the lights up a bit just to play it safe. I wouldnt worry about it if that is the only spot

Thanks guys that must be what it is