Light markings on new leaves.

I saw those during the early seedling phase as well. I worried that it might be fungal, but I think its simply where my leaves came into contact with some soil that got blown across them when I was adjusting the fan. Though the other possibility is that it could be a fungal infection. The one thing I worried about when I had leaves like these was Septoria cannabis, which is a fungal infection that can look like this when it begins. You can do a search on its symptoms and compare images to your plant, and possible causes, to see if it looks like you may have it, then treat it if you do. If it is, you caught it early and these can be usually dealt with completely with no long term ill effects if you catch it early and deal with it swiftly. In my case, I couldn't be certain that it was but couldn't rule it out so I took some recommended measures to treat it in the early phase: I turned up my fan to generate more air across the leaves and reduce humidity pockets (this caused wind burn, though that's minor) and also added some vinegar to the tank of the small humidifier I had in my tent for seedling stage (I decided against more drastic steps like misting the leaves with something) to convert that into a very weak vinegar solution (some mist from it does land on the plant). After a couple days it disappeared. I couldn't be certain it was Septoria cannabis, but if it was, that took care of it. Two places I can think to begin looking.