Seedling Autopsy

The problem seedling from 12/14 is on its last legs, so I wanted to get some ideas how to avoid this in the future.
Three other plants are rocking out and exploding, so I am trying to nail down things I could have done differently to cause this plant to die.

I understand this is subjective, but have attempted to provide any relevant info. Thanks!

BC Bud Kush
1. 400W MH at 24" above plant tops in 4x4x6 ft tent. Switched from 24/24 to 18/6 on 12/19.
2. Watering was f**ed up for all plants through 12/19. Ph was mid to upper 7. Since 12/19 I have the water Ph at ~6.8.
a. Initially thought was over-watering, but soil was dry, to slightly moist, at 1 knuckle depth in every test case.
3. Same soil for all plants (Vigoro Organic) mixed with perlite and dolomite lime.
4. Temps are staying low since 12/20 (avg 76 w/lights on).
5. No nutrients given to seedling. First nutrients to healthy plants 2 days ago.

Here is the progression of illness:

Day 5 from Germ (12/14, [79F/34% Humidity]):

12/16: Watered all
First sign of trouble (12/18, [81F/28% Humidity]):

12/19: Watered all and flushed this plant
Continued problem (12/21, [75F/25% Humidity]):

12/22: ​Watered all
Unlikely recovery? (12/24, [77F/29% Humidity]):


Two plants that appear to be kicking ass and have had the exact same environment (2nd plant is White Lavender):

...yeah man, i don't know what level of experience you have so if i say something you already know don't take offense.

ok, the first thing that jumps out at me is that the pots are too big for seedlings, with that much media the rootzone will retain moisture for too long, you have no rootmass yet so what you're seeing is i believe signs of overwatering.

you could also use a fair bit more perlite in your mix which would also help them dry out quicker.

the last thing i'd say is that sometimes you just have to go with it man, don't overthink it or it'll drive you bananas, some seeds, some plants, just lack vigor, if you're doing everything the same and one plant out of many is suffering then chances are it's the plant and not you.

...in this case though, all of your plants are showing signs of stress and caused i believe by the too big pots.

peace, bozo

btw, here's a few shots of some of my starts where you can see i start my beans in 9oz solo cups and they actually stay in these cups for about a month.

First grow here. Been rolling with it up until the seedling started to die lol.

Even the two last pics are showing stress?
I've been checking moisture by hand and with a ph/water probe. By the third day after water they are dry.

The light may be to intense for your seedlings, have you tried running them with cfls untill 2 weeks old?

I think these guys have it. Pot too big and I think the light is too close. Very nice clones and seedlings bozo. match