I still don't know what's happening to t...

Cotyledons are not leaves, their only purpose is to protect the growing tip as it pushes up out of the soil. After the seedling emerges from the soil, the cotyledons job has been done, so they go yellow, die and drop off and let the true leaves, the serrated ones, take over and do their job of making energy for the plant to grow. All this is a normal process in the life of a cannabis plant and there is nothing that can be done to make the cotyledons stay green for more than a few days. So, no need to worry or do anything. Hope this helps, Organoman.

Don't worry. They usually do that at some point. To treat nutrient blockage pH must be correct and the soil can't be underwatered or overwatered for much time. If the rest of the leaves are ok you're ok! 👌

Thats absolutely normal dont worry! If the big leafs start to do the same THEN you can worry.

If its a new good soil, you don't have to feed plant for minimum 2-3 weeks. If its a bad soil, its also will not cause serious deficiency on first weeks. So, I hope you didn't much problems with nutrients and now if soil is dry give clear water and wait for 5-7 days. If already gave, also wait for minimum 5 days.