or the soil got to hot
Keep an eye on your ambient temp. feel the soil in the middle of the day cycle. If it feels to warm, put them in a larger pot with a bunch of soil, it'll help keep the root zone temp lower. This is where you must be carful not to over water. In a typical veg room, you may have to water once a week for the newborns
Seed starts don't need any nuits until they are past the sprouting stage
Wait until the little round leaves at the bottom dry up or drop off before giving them anything but ph'ed water and benaficials