I have noticed brown spots on a leafes, what is it...

Without a picture it's pretty hard to guess, but brown rust spots sounds like lack of calcium.

Hey man I checked out your photos Good start I think what your seeding is early signs of over watering. When you have a small seedling that the roots are not all the way to the bottom the pot and filled put nicely you have to be careful when it's smaller to only wet the soil abrely around it where the roots will reach. Them next time water a little more and a little further from the plants eventually you can water around the edge the pot and let the water almost get to the bottom and them wet the bottom the pot in water just a little usally after that time the roots are pretty sturdy and u can water fro. Top and get soil wet all the way thru. Make sure to let soil get completely dry between waterings you will see plants healthy for a period then when soil gets dry enough they will start to wilt that's what your looking for the leaves to sag about 15% of their normal positions when ubwater plants when they super want water they will thrive I would wait a week or so to add more nutrients just to be safe the plant is quite small

Are you able to give a little bit more Information? Picture would be best I guess? If you talk about the Amur Gelato Auto it looks like the leaves were wet at some point, if it is not just water it could burn the leaves a bit. No worries right now plants look good give it some time.