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!
What my room looks like when you enter

What my room looks like when you enter

Hosta Damage

Hosta Damage

After the rain

After the rain

Look at this DIRTY SMUT!

Look at this DIRTY SMUT!

tomato bottoms turning black!  and bumps on the stem

tomato bottoms turning black! and bumps on the stem

Esperanza

Esperanza