Help! Easy diagnoses for anyone, i just can't see the pictures in the sticky post

My plant is about 3 weeks old. Theyve been in seed starter soil and I've only fed it once with a very mild solution. Is it just the beginning of a deficiency?
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The leaves are looking a little yellow and thin, should I just feed it again?

to early to feed nutes 4 weeks seedling then you can feed during veg let it grow on water

Ok ill wait and just let the plants get used to the worm castings in the mix first.