Is that powdery mildew?

I agree with numbers, less like WPM and more like mineral deposits. If it washes off your good. Good Luck!

looks more like drred up minerals from a drip of water that got on the leaf. You'll know soon enough.. if it 'grows' you know it's alive and not dried up minerals. It would also be fuzzy not flat. if it does 'grow', throw it all out. you are early enough that that is the best way to go. neem does not cure it. nothign cures it. not even professional grade antifungals you can only buy if you own a large commercial farm. On a larger plant you try to cut it out and pray it doesn't spread, but by the time you can easily see it, it's already in the air and propagating.

bucket.growdiaries.com/static/post/photo/198511/8876199_9050f08863533b5a9024d5218e2c021f_big.jpg

Hmmm i agree with most growers looks like a water droplet stain though if you are certain this is not the case then something else has got on there some how. should be fine just be patient :)

I'd say it's not wpm, most likely where the leaf got wet then the light fried it.

No it IS NOT mildew, just looking like a water droplet mark. No need to spray it with anything or wipe it with anything or start again ..........and neem would not help even if it was mildew. There is nothing that you need to be worried about, at all.

Unless it's in an environment where more is present, it's unlikely WPM. It's more likely to be a dried drop of water from feeding or condensation. Wipe it off with peroxide and monitor it for signs of returning.

If its really not spray or condensation mark, then get rid of it , wash with soap and hydrogen peroxide all grow area and restart. There is no escape, especially in such young plant. Rub that spot with fingers, if smell is mouldy - its WPM. Do not touch anything, go straight to wash hands. Then get rid, clean everything and restart.

spray Neem Oil on plant it will help