Pure Kush - First Indoor Grow

Seedlings are struggling. My guess is it's from over watering substrate with vermiculite in it but I'm not 100% sure. I've been fairly moderate with water. If they were in regular potting mix this amount of water would have been okay. Next time I'll start them in plain potting soil. I also thought that maybe there was a nutrient shortage because I'm using 25% coco coir but actually this seems unlikely. In any case I put a bit of extra soil on top of the pots. Despite the browning off this week the stems are still really strong. I'm still confident they will recover and just need time. The temperature fluctuations of the last week might have had a negative effect.