Plants are ok?

They look good, The light green tops are nothing to worry about that’s usually new growth or a slight light stress. If you keep temps and humidity stable like in your photo 24 °C / 56 %, you’re spot on. Just make sure the light isn’t too close and keep feeding as normal they look healty

First of all u need to up P a bit +50 ppm The lime one shows sings Ca deficiency, the right one Mg excess Also could be to much K so i,d lower it for a week if u see burnings on top leaves

it might not have developed as strong as the others. Seeds are not clones. Or maybe its medium is slightly off. No diary mean its all speculation and nothing based on facts.

Do you leave you door open on your tent? Could just be growing slower than the others from lack of reflective light if you do. Went through something similar with a plant i kept in the exact same spot