Don't worry too much over seedlings, I had to learn that the hard way and took me a very long time. Less is more when it comes to seedlings. There are a few basic requirements that a seedling has, once met and maintained, the plants really grow fast. Humidity needs to be high like 70-90%. Air slightly cooler than the roots are. roots aim for 76-78F and air is a few less. U need to let the soil/media dry out some. Not entirely bone dry but from 1-10, 1 being bone dry and 10 being just watered, you are looking to at 3 before you water again. Don't feed that seedling ever until it has used all it's stored nutrition from the embryo and cotyledons. Only when the leaves (cotyledons) have yellowed, browned, shriveled or fallen off, only then do you start a feeding schedual or transplant into a fortified media. The seedling has everything it needs to establish a roots system and 2-3 sets of internodes.