My first baby

I started out in backyard shit soil that was made out of silt, sand and some other not so good stuff. I used the napkin trick to get me started and planted in a solo cup. she sprouted a couple of days later, I added some great white to the soil and watered her. about a week later she grew her first set of leaves. I made the mistake of trying to feed some nutes (general hydroponics,6.5ph 400ppm) which was too early I feel (about 2 weeks after sprout). she Kept growing but her first set of leaves started turning yellow at the tips. thank god my ocean forest came in so I transplanted into another solo removing the backyard soil from the roots. I thought that would fix the problem but my first leaves ended up still yellow and now has brown spots on them. I think it’s nitrogen deficiency idk. Good thing is it’s not spreading upwards. thanks I’m advance for your help