did you shake out your rockwool before you put seedlings in?
IMHO; start your light at 30" and move 6-8" closer every 2-3 days until you see plants perk up then keep them at that relative distance. they don,t need a lot of light at first so Fluoros are the best choice...right on top of them if you got fluoros, if not see above.
Zandor; I had a thought...you grow using drip; right? From the way you explained the nutrient buildup in the rockwool I realized that using drip would cause this buildup...that said...using bubblers, I have found that if you pre-soak in the same ph adjusted nute solution overnight.put the rockwool in hydroton and leave it alone; it get's fairly dry and everything stay's sweet in the res...but if you flush the rockwool thru the top it rinses the rockwool, your res ph goes apeshit!!! the rockwool becomes wet again and you experience nute buildup problems and moisture problems.
Thus, IMHO: Shake rockwool out (like shaking a paintbrush) to get rid of extra moisture, and do not flush rockwool after putting in grow medium...add all nutes/ph water by pumping it in or lifting whole top and pouring it staight in.
Does that sound right, yes. of course IMHO...latewood