Lacebark Elm Issue

[Bayers]

I've never planted trees before. In early December I planted some Lacebark Elm seeds that I collected and I had some sprout. They were doing well and then the past few weeks they've begun having yellow leaves and even a bit of curl. I know it isn't from over watering because I'm very careful with that. They're planted in peat/perlite with osmocote plus. I've read that yellowing can be caused by lack of nutrients. Should I add more osmocote or do something else? Or could it be that they were getting too much light? (It was winter months and I had grow lights on almost constantly.)
I appreciate your input.
I've attached some pics.

 

[Wrangler]

That’s a cool project. What is the condition of trees since the day you posted. I wonder if soil test lab would look at your potting media and give you suggestions. I hope they do well!!!

 

[KTSmith]

I think that the top image shows interveinal chlorosis, particularly in the younger leaves. Now, apparent deficiencies in nutrition may reflect an insufficient root system rather than actual insufficiencies in the soil.
This pattern of chlorosis is often associated with inadequate iron, magnesium, and/or manganese nutrition. Before reaching for the fertilizer, understand that a relatively high pH (from about neutral on up) renders those elements unavailable for root uptake which can then render the foliage deficient even with plenty in the soil.
My response assumes that the OP has checked for mite infestation (use a hand lens), particularly on the lower leaf surfaces.