Looking for some help, bagseed CFL grow roughly 3 weeks in

Hey RIU! I could really use some advice. This is my first post and my first grow and unfortunately it's because I've ran into some problems. I'm currently about 3-4 weeks(one plant has a week over the others) into my cfl grow and over the past 2-3 days I've noticed yellowing of the leaves, mostly on the tips, along with rusting(only on largest and oldest plant) and leaves curling down. There are also some purple stems/branches but not on the biggest/rusting one. I am using MG organic choice potting mix soil. I have four plants(from bagseed, unknown strains) in 6 inch pots under 4 CFL lights (2 2700K, 2 6500K, all 23w/100w equivalent). Until about 5-7 days ago they were only under the two 6500K. They are receiving 18/6 lighting. I'm attempting to LST three of them. I water every few days when the pots are light and the soil is dry. I don't have a means of testing the PH right now, but plan on buying one today. Same with a thermometer. Although my guess is that the temperature and humidity are ok.

So I'm guessing it's a nutrient lockout due to imbalanced PH. I originally thought it was some type of light burn but I'm using CFLs and they were only about two inches away. What do you guys think? Also, I've read many mixed opinions of MG soil, and it seems it works well for some but others swear against it. Is there an easier/better soil I should look into? If I keep the MG should I be looking into buying some fertilizer or just letting it ride with the time released nutes? Thanks in advance, happy reading, growing, and of course toking everyone!

Calm down bud, your plants look just fine. I used to worry about the tiniest little stresses here and ther when they're just starting off. Your plants look quite healthy, the slight burn could be from many different things and if is continues in the next week than perhaps you should worry but otherwise I would chock it up to lower leaves dying. By the time you flower this baby, that leaf will be way at the bottom and the least of your concerns. As for the yellowing, it doesn't look to bad yet, if it starts to wilt with the yellowing you would be in serious trouble. Just slowly, and I mean slowly add more nitrogen or "grow" formula if you use liquid nutes, with each feed and I'm sure you'll be fine. keep posting pics, I'll come check things out soon! good luck

Thanks for the reply hood. I had lower leaves yellow and die off already but havent had the rusting that is currently progressing up my plant on the tips of leaves. I guess that's why I'm a little panicked. It started at the lowest and has now made its way to the top leaves, it's gotten worse since yesterday. Didn't get PH test kit yet but I'm on it today.

I tested the pH, it's too low. Going to transplant into larger pots and add dolomite lime to the soil. Plants are looking worse. Much more yellowing and rusting. Leaf fringes are standing up strongly on one of them. Hopefully the lime will help. I also did some shopping and added four more 23w cfls. I'll update with pics tomorrow.

Transplanted into larger pots and added dolomite lime. Looks like the roots needed some more room too. Hopefully things start looking better soon. I'll post pics when I have my camera.