I agree, that soil is too rich for seedlings. You can see whats going on, they no like it.
I use a very light organic seedling mixture. 2 parts soil 1 part worm castings, that is it. Go crazy with castings, they wont burn and they buffer ph somewhat. And I don't have to worry about deficiencies for a few weeks. Theres enough for seedlings to run along with. That's basically it. Just a bit of perlite for drainage and so those young roots have an easier time getting established in nice fluffy soil mixture. Easy peazy. From sprout until the cotyledon yellow and get crispy and begin to fall off. Besides just water they are pretty on much auto pilot up to that point. Then I introduce growth ferts. Or transplant if required, then introduce additives.
Initially, for the first few feedings I usually will half the recommended dosage, then half it again. Less is almost always better. Especially true in these early stages.
Its pretty hard to pull back after too much goes in and causes adverse effects, burning or otherwise. Flushing is about the only option. Unless you can get away with transplanting. But it interrupts everything. Its a necessary pain in the you know what when its easily avoided in the first place. Not as bad early on but when its late in the game it delays everything and throws the schedule all out of whack. Perhaps PH as well.
With larger vegging plants and plants into there flowering stages. At most I stick by recommended dosages or a touch under. Very seldom I will go above it. Once maturation is reached you gain a feel and it becomes easier to gauge things better by how the plants are looking and responding.