The yellowing is from nutrient deprivation. Your plant is starved of nutrients because it cannot breathe. Remove the massive amounts of water around your roots and follow a strict regimen. When you think the plant is thirsty, wait another 24 hours, and then water. Ensure that the roots are forced to search for water.
I was told one thing about growing in soil when I first started growing: "It is VERY hard to underwater your plants, and VERY easy to over water them"
As well, I can tell you're a new grower because you're in the "over" phase. Try not to over-water, over-feed, over-analyze, over-manipulate, over-stress your garden. New growers tend to over analyze everything and try to impart a million safety measures at once, which in turn slow the plant or kill it. Also, you have no reason to LST that thing so early. Let it get a little sturdy, and you and ease your way into training the plant through physical stress. Right now, that thing just wants to grow and you're not letting it. Set it under that light, and do not touch it for two days. TWO DAYS! NO TOUCH! Haha. Should pull through just fine