Yellowing seedling

yeah.. give her normal concentration in coco. At least around the plant, not the full pot, if larger. match canopy, maybe a bit more. probably good to rehydrate outer area too but not with nutes, otherwise you end up with buildup where roots don't exist. seeds are good for a while. watch the cotyledons for earliest signs it needs more nutes. typically, coco is buffered too, so you typically have a little in there to start. see those tiny leaves fade a tad, start your regular feeding relative to plant size.