Any know what this is ?

What medium are you running and what is your ph as well as nutes?

Sounds like heat stress or light wind burn, especially if the fan was closer to that plant. The brown spots could be from that—try moving the fan a bit further away and monitor if it improves.

looks irrelvant, i'd be more concerned about the chlorosis on your new growth. Paling petiole-out pattern indicates low s, possibly too much p/k .. leaf symptoms are not discrete. there's a potential micronute cause or 2, but those are rare. As far as the fan goes... just get a little jostle to the plant. it does not need to be direct wind from fan to do so. You really don't need much at this stage. soilless context only - 100ppm S is a good starting point. observe and adjust from there. if in soil, you want to be a bit more patient and observe how it progresses to more confidently diagnose it.

Hey 👋 For me it looks like you dropped some water, and your LED burned that spot. It happens pretty fast, but nothing to worry about. As far as you did not use fertilizers yet (which you shouldn’t if you used pre-fertilized earth) there shouldn’t be some issue with fertilization. From my point of view it’s nothing to worry about at the moment. If those spots seem to appear more often you should just repost 👊 Hope that helped. Happy growing 👊🍀