Hello, I'm new to indoor growing and need some advice. My 3 week old plant has stopped growing and is drooping. It hasn't shown any new growth in over a week. The PH is fine 6.5-7.0. Was using Enriched Miracle grow soil until today, i transplanted to ProMix HP. I may have over-watered but i'm not completely sure. The bottom leaves are starting to turn yellow. It's on a 18/6 hour light cycle under 400w MH. Also I had already waited 2 days for my soil to dry before i decided to transplant and i didn't see any sign of the plant recovering, that's actually why i decided to transplant. I also always leave my water sitting out uncovered for 24-48 hours to rid itself of any chlorine etc. Also when i transplanted into the Pro Mix HP the roots were what seemed to be gathering on the bottom and growing from the bottom towards the top on the sides of the pot, not in the soil. And also the "knot" was fairly tight. Is all that normal? Or is that a sign that the roots are not getting enough oxygen? Or could it be something like "rootbound"? I thought it seemed weird. Another question i have is in other forums on this website i read that when your leaves start to yellow especially from the bottom up, that usually it means i have some sort of nutrient deficiency. Possibly not enough nitrogen maybe? Any thoughts on that? Any advice or suggestions would help. I have uploaded Pictures.