dying sprout in hydro system

Hey all. I'm having a problem with a grow and I could really use some advice. It's my second grow ever and the first one wasn't too bad. The second one started out just fine. Set up = 2 bucket top drip system with clay pebbles, seed in rockwool, adjust the pH of the water (right around 6), 2 T5 veg lights (worked quite well with the first grow) and let it grow, right? Well, it sprouted after just a few days and had a couple leaves on it and looked good, then a few days later it started to turn brown. I thought it was getting burned with the light so I moved the lights further away, but each day it gets worse. My most recent theory is it's getting too wet, even though it's a hydro system. It just looks really saturated all the way through. I moved the drip "hose" so it's not dripping on the rockwool anymore. Instead it drips next to it into the pebbles and I'm hoping the rockwool dries up a bit and solves the problem, but I don't know if that's the solution. I also noticed that the rockwool is turning brown where the water drips on it. I'm guessing it's just cuz of some grit from the clay pebbles., but any thoughts on that? I would really appreciate some help with this. I'm new at growing and after the first grow I thought I had the basics figured out, but I can't get a handle on this second one and I really don't want to lose it.

Any updates,your right to move on to the pebbles,roots can grow quickly outwards,aswell as downwards.