Help me diagnose my plant problem?

Hello, newbie here.
I have a crowded tent, 8 plants/3gal pots and it seems some lower leafs that may not be getting light (?) are yellowing, some with spots, and are withering off. Also, I noticed some slight nute burn on tips so I flushed the girls out, a few days ago. Still seeing the leaf problem.
Some notes: soil grow with ff trio nutes + cal mag, ph around 6-6.5, 750 watt LED, Mandarin Cookies v2 around 75 days from seed
I just realized I have not ever been watering to runoff, and after finally seeing slight nute burn+ reading more I understand why it is important to have SOME runoff and will water like that moving forward...
my question is what is causing the withering & how can I correct it, thank you!
Should I remove some lower leafs? I originally topped some, Fimmd a few others, and left a couple to just grow- thinking I would kill maybe half, and instead they were thriving, but crowded. I'd like to see this harvest through!

They look fine to me. I don't water to runoff because I feed light and they are only in the medium for 2 months or so. They are a nice dark green. You could probably back ff some N if they start looking worse. So far I think they look fine Crowding is a tough decision.

Good job! They look nice and healthy.