Grey Spot on Leaf

I am growing some Anesthesia Auto indoors, currently its the begining of the third week since germination. They get around 600 ml of 6.5 ph water every two days. My growing substrate contains sphagnum peat in blocks H2-H4 and H4-H6, medium coco fiber, lime, calcium nitrate, perlite and NPK. pH 5.5-6, EC 1.4, Organic Material 65 %, Real Density 250-300 kg/m3.

Today I noticed a very odd looking grey spot on one of theinitial leaves, here i post 3 pictures, the first there is no spot which was taken at 2 am 25th of sept and the second is at 5 pm of the 25th, the third is a close up of the spot.

Any ideas what it could be? Is it mildew?
Thank you.
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I dont know if there is any reason to be concerned, but any input is appreciated since this is my first growing experience

Can you just rub it off with your finger? If not, probably not mildew or mold. The plant is not old enough for notes in my opinion. Wait til she is 8 or 10 inches tall/about 2 or 3 more weeks if she isn't that tall by then. Should be fine.

I wouldn't worry about that.

These always help