Hey they look alright. I think the problems you are experiencing with the leaves are actually nutrient burn, not a lack of them.
Maybe your miracle grow contains ferts that your seedlings don't need yet.
Seen so many grow logs where they use MG time release nutrients and their plants go fine for a few weeks then begin to wilt/burn/die off.
Here are my plants around 4 weeks.
amazingly, the one on the right is the one that was given a small dose of nutrients.
The one on the left is in a sterilized potting soil with no nutrients or additives what-so-ever. 2 days prior, they appeared identical!
So in my limited newbie opinion, don't add unnecessary ferts, you'll only mess things up, young plants don't need them.
The brown spots on the leaves, trim them off.
If you have leaves looking like this:
Sadly the plant cant use the damaged parts of the leaf, and will not repair the damage.
It will only continue to grow new leaves. Trim off the burnt parts before they worsen.
The plant really won't mind, as it wasn't using the dead, dryed up parts of the leaves anyways.
I thought, "wont cutting the leaves cause them to rot/decay around the cut edges" Gladly, i thought wrong.
