Newbie grow, plant bottoms turning black

Hey there guys. Super newbie here. First time planting seeds ever, and they came up now they’ve been sprouted out of the ground since June 2nd-June5th (June 16th today). One of the plants, the runt of the litter I would say, has been sprouted since the 2nd, it has more leaves with the set on it having 3 prongs. That one was the only seedling out of 8 seeds I planted out of that batch that made it. It’s super short compared to the other ones and it’s been growing slowly, way slower than the others. I’ve been using a little Cal Mag since they came up, not much, even less than what I’ve read since I wasn’t sure if they could take it, (now I don’t think I should’ve). I’m using extremely good RO water which is why I’ve been putting calmag in. Just wondering if somebody could reply I’ve been reading and I can’t see anything like exactly what’s going on here. It’s been like this for roughly 36 hours. I transplanted it and separated the one that looked sick into a different pot. I’ve flushed the pot a couple times to try to get rid of the nutrients if that’s the case. Not sure if it’s molds, I gently wiped the leaf and nothing smeared or came off. They’re just turning a dark color on the bottom, hopefully somebody has some ideas, I haven’t read anything that is specific to what mine looks like. Thanks guys

I think it’s been over fed and overwatered. Plants in soil, assuming you’re in soil, don’t need any nutes until 3-4 weeks in. They also only need small amounts of water, like a turkey baster amount around the stem, not the whole pot. I don’t know what that exact issue is, maybe dampening off of the roots, and I can’t tell you if it will recover, but definitely ease up on any nutes and your watering.

It's hard to tell from the pics but is there any chance it's genetic? What variety are they?

What soil are you using, what kinda light, and distance, etc. All this is needed for anyone to make an accurate guess. My guess off of zero information is they started to stretch the first 72hrs or so, you brought the light closer. And have been overwatering them the whole time in FFOF soil

Hey there guys thanks for input. On the plant that was doing it, I flushed the pot after transplant and moved lights further away. The black on the leaves is about 50% what it is yesterday and the black is going away. It was probably “sunburn” I’m guessing. It’s my trial and error grow. I get the seeds from my buddy who has a good grow. He usually goes out to California for some of the strains, he picks up clones. Thanks guys