First time grow - day 6 seedling stage

Looks normal! Start feeding around day 20 but depends on the size and need of the plant. And how your soil is 🌱👍

Hello The white vein is pretty common, not usually a disaster. But sometimes it can be down to heat or light, but without any specifics it'll be a hard one to call. The yellowing on the 2nd one made me first think of that mutation where you get the two toned leaves, Variegation. But it may be more likely the soil is too hot, or some sort of unhappy roots(ph or over/under watering). Because the rest of the 2 seedlings are so deep green i wouldn't recommend adding any nutrients right yet, give it another week or two and see if they outgrow this. Happy growing. ✌️

Mg deficieny takes weeks to show.. same with Ca. as they said in national lampoons Vacation, "You're going the wrong way!" Water throroughly, always and with runoff of 20%. Wait for top 1" to dry. Not doing this might be the cause. check pH... it's highly unlikely it's a deficiency.. the seed is good for 10-14 days on its own.. the only thing you can cause is lockout.

Same seedling. Looking great! 2 is now 1 👍👍 From The White House.

la 1 tiene buena pinta y un color agradable,la 2 creo que es carencia de cal-mag, un riego por semana y listo, yo empezaría con abono(siempre por debajo de los parametros que te dice la casa e ir aumentando progresivamente con medidor de ec y ph) y cal-mag en el siguiente riego,saludos y suerte @kevingrow

Plant 1 looks fine. Plant 2 looks like its dealing with ph imbalance or ph fluctuations. Definitely looking ph related. Happy growing and stay lit fam