Lower leaves withering, slow growth

The following image looks similar to one of my plants and I've been concerned for awhile.
https://www.rollitup.org/attachment...672d1230409645t-my-1-week-olds-withering-.jpg
The image was posted by another user. Mine is much shorter and bushier and I have pretty good lighting on it.

I thought this plant was going to die when it first sprouted because it's first set of serrated leaves were very deformed. They curled up and now they appear to be dying. I did notice that at one point when I was watering it less the withering stopped and growth improved but I'm not so sure that's the problem. Veins are pale green to yellow so I was thinking a magnesium deficiency and added small quantities of epsom salts about 4-5 days ago. This plant is about 10 days old, perhaps 3 inches tall with it's fourth and fifth sets of leaves coming in along with some branching. I have them all in 6 gallon pots (so it will look smaller then it is because the pot is huge) with miracle grow soil as depicted by seemore bud's book (though I had been growing like this before I read it, I thought I'd just cite a more credible source).

When I water, I don't completely soak the soil. I typically put a cup or two in there and wait 3-7 days to water again. This has worked extremely well for my other plants, the oldest of which is 16 days old, over 5 inches tall and extremely bushy with five fully developed sets of fan leaves. The attached image is of my actual plant. It's not the best photo as I took it with a borrowed camera to show the temp and humidity of the grow room. The other images is of my larger healtheir plant. Despite all appearances, the larger plant is not stretching. The space you see there is due to branching. Closer examination reveals that the main stem is almost entirely obscured by side growth.

look fine to me, dont freak out

This shows it much better. Took this today. You see that? I haven't watered it since Christmas morning and though the condition seems to be getting worse, I'm at least seeing some new growth now. Also, the bottom of the main stem is turning white. That can't be good.

It's taking these leaves a long time to die. The plant is about 12 or 13 days old and that set of leaves has been dying since day 1. Weird huh? The soil feels mostly dry, though it's def still a bit damp 2-3 inches down. My biggest plant is getting watered on the same regimen, is MUCH larger at 16 days and continues to grow new sets of leaves daily. It's thriving. It doesn't have this problem and in all honesty, it's getting only slightly more water.

Here is a few pics of the healthy plant today, grown in the exact same soil, under the same lights.

looks like a slight ph issue.. it looks fine its definitely not dying.. some plants grow faster than others its just genetics.. i would make sure your ph is spot on and just keep on truckin man.. they look good dont worry about it. and the whitening at the bottom of the stem is pretty normal on some strains.. its almost like bark, just means it is getting stronger

I was wondering about that but am still too inexperienced to be able to discern. If it's PH I'd bet it's too basic. For the first week and a half ALL of the plants were watered with tap water. I ran a PH test my tap water the other day and it said the chlorine range was in the ideal range for swimming pools, though I did at least have the sense to leave water sitting out for 24 hours before using it. Geez! The water had a PH that was so high that it was almost off the scale for my particular kit (about 8.0). The MG soil is known to have a lower PH but I think the water sure drove it up.

I'm not feeding them nutes aside from whats in the soil but I think I might add some vinegar to my distilled water to try and lower the soil PH some more. Right now the water I'm using is between 6.5-6.8 which would normally be pretty close to perfect, I think. I do think that most of them are doing very well considering that they were tortured with tap water for abit. Fortunately for them, I do have some grow experience or else maybe they'd be much worse off.

Thanks for your reply!