Yellow tomato leaves

Yellow tomato leaves

So, my seedlings are about a month or so along. I have my little guys under a flurescent light while they get strong and I am too lazy to get the containers ready, and they're developing a problem: the topmost leaves are yellowing and curling up from the sides. I'm certain it's a nutrient deficiency of some sort, and not a burn from the light. What makes tomato leaves turn yellow, and how do I fix it? If it helps, all of my varieties of tomatoes are doing it, including romas, super sweet 100s, some German and yellow heirlooms, and some pear tomatoes. They were stared in peat pellets, and later moved into small Jiffy pots. Thanks!
Healthy Cheap Eats Part I: Parmesan Fish Sticks

Healthy Cheap Eats Part I: Parmesan Fish Sticks

Update on Wild Thing

Update on Wild Thing

Thank you!

Thank you!

From the terrace…

From the terrace…

Im so excited…I just cant hide it

Im so excited…I just cant hide it

Plant ID

Plant ID