3 Bears OG

This plants seems to be slower than the rest, well see how it comes out. Started giving it nutrients every other watering. 1/15 - looking ok. had a cold night, -20 outside so the tent got humid and I found some mold on the top soil. I scraped it clean, added some new dia.. earth and covered with pantyhose to block the fungus gnats. Plants look ok but have some spots. Not sure what's going wrong, maybe just the humidity and cold. I tested the PPFD with and app and found 16-24 inches to be way too much light though I don't know how accurate it is. Lights need to be about 36in+ away for the correct numbers. I also ph'd my water and did nutes according to the bottle and watered until runoff. I plan on just sitting a few days and watching how to plants progress as I don't want to stress them more if i'm doing something wrong. Just trying to lock in temperature around 74F and Humidity around 50%.