Any idea on what nutrient deficiency I'm havi...

Hi there NiagaraFalls , the burnt tips on the leaves are a sign of nutrient excess and it's called nutrient burn. next time i wouldn't use any nutrients until week 3 or 4 if you can avoid it , as you can see it's not necessary to add more juice with store bought soil that might already be rich. For now water with plain water until the problem stops spreading probably a little over a week. The most affected seedlings will be stunted forever and will grow more slowly than the rest, just a heads up in case you need to make a hard decision. Hope this helps ! 🚀