Seedling issue

Soil looks really dry too

Looks like magnesium deficiency with the green veins and yellow margins. Did you add dolomite lime to the soil you're using? Looks like you're using regular potting soil. You have to add CA and Mg using Dolomite line but you need to get some Calmag in a bottle and water it in along with whatever fertilizer line your using. Also Dr Earth Tomato and Herb and Dr Earth Bud and Bloom ferts are nice and easy. Dr Earth has an organic Cannabis feeding schedule on their site.

You need to provide more information about the grow so we can help you more efficiently!