Stems becoming red. I didn't use any nutrients yet. Should I add a little bit of them to water? Water pH is about 6.5. Do the leaves look ok?

She looks fine, maybe start nutes in a week, the first 2-3 weeks generally don't need nutrients or much light

I wouldn’t start to worry too much. I looked in your diary at the type of soil used and I’m not familiar with that. If it has nutrients in it, you should be fine for a bit. It almost looks like a soilless type mix tho and if that’s the case there’s no nutrients in it at all.. so I’d try to figure that out and that will let you know if you should feed any. If it does not have nutrients than you should begin feeding at this time. The red stem can mean several things, not all bad. I’d relax and find out about that soil and go from there

LED lights can cause stems to go red.