overwatered & over-nuted my 2cents
edit:
that looks like Miracle Gro soil too. MG is cool, but you need to add some perlite to the mix before you add plants to it, which it looks like you have done...
also I dunno how much this helps but what I do is saturate the soil in tap water for about 2-3 days while my seeds are germinating, then I start seedlings off in jiffy cubes until the roots are about 2"-3" sticking from the bottom, that way I know the seedlings are mature enough to handle the preferted soil, then I transplant them into the soil, water once more, then wait for the soil to completely dry out to water them again. I only watered two or three times my entire vegetative cycle. I've must've water at least seven times so far in my flowering cycle.
what you should do is give it a really good flush of pH adjusted water (6.0-7.0) and let the soil dry out for about 4 days, or until its dry about 1 1/2 inches down, then the next time you water, just water until about 30% of the water drains out of the bottom, let it dry out another 3 days and then do the process over again.