Whats wrong with these Auto Norther Lights

So I have three NL auto and three gelato autos. One is just looking like its going to die, the other is small and starting to get yellow tips. The last NL is small but looking ok, just a little yellow tips. My three gelatos right next to them look great. They are all 18 days old. Whats wrong. Ph rain water at 6.2, soil is ph 6.2, no nutes, I haven't watered in a week because I though maybe over water. I though maybe light burn because I was at 6500 lux at those plants so I move them away to 4,000 lux last week also and its getting worse. Again the gelatoes next to them and all the same conditions doing great. Temp is 78 day and 69 night with 20/4 and 70% humidity. Air circulation is every 10 min. And I have a fan on all the time just to keep the air and humidity even throughout. Any ideas? I know NL are a cooler running secies and can handel lower temps. Maybe 78 at 70% is to hot??? First three photos are the NL last three are the gelatos.

What medium are u using it looks a little dense?

3 parts compost, 3 parts peet moss, 2 parts perlite, 1 part vermiculite. Its supper lite and airy. The one plant died. I pulled it and the root was about half an inch long, but the plant had 6 leaves. I think just bad genetics. The rest of the northern are doing ok but they look like they are a week behind my gelatos.

You be right then mate good luck