Flo n gro

So this is my first hydro gro and I've over come my first obstacle which was cloning. I failed at two attemps then built a aerocloner and had 100% success. So that said I figured I'd spend the money on a flo n grow. After mixing up 30gal of nutes I put 6 clones gently in the clay pebbles. After 5 days my stems seem real dark and hard and they don't seem to be taking off well. I'm using house and gardens. A+b, multi zen and root accelerator at the moment. Under 1000 watt hps. Any ideas why my stems are hard and dark and not healthy. I feel like giving up on hydro but u guys have had the right answers for me in the past. Any ideas would be appreciated

Pics would go along way in determining if something is wrong. Its possible they are growing roots to support upward growth, and the stems are just getting stronger along the way to again support upward growth.

Not home for pics right now. But I did notice a lot of brown residue on the inside of my baskets. Maybe I didn't rinse my pebbles good enough. I rinsed them 3 times. Would that cause a nutrient lockout. What would I do about that

it can ruin your pump. make sure you clean before you start a new batch of plants. What amounts are you feeding? feeding 30-50% of the label strength is what i would do for General Hydroponics. Do you have PH level for your reservoir?