What is wrong with this seedlings???

They were planted 14 days ago... but tap root was a little bit dry, i rehydrated them and when tap root looked good and hairy planted. they had it difficult to create a good root system it looked and when i transplanted from solo cups to 1/2 gallon pots some 4 days ago the one in the left had roots but only a few and short... the two in the right better but not 100% healthy. one is already showing roots from the bottom holes of the pot so i assume slowly their roots are growing and becoming healthier. the problem as you can see is not only that they are understandably growing slowly but that they are turning yellow and have burned tips and edges...
i have watered last time three days ago with tap water like 280pp with just a little GH FloraGrow( like 1/4 strength) total was like 310ppm on 5.8pH. What can it be??? lights are some led cobs which i moved away even more from the plants. Can it be light burn? Nute Burn? or something else??





Any input is appreciated...

Being a soil grower exclusively, I cannot say with 100% certainty. But, if one of my little ones looked like that I would be thinking nute burn.