Thanks man.

I looked a little closer at the plant and right where the stalk goes into the rockwool it has turned black and really thin. A few weeks ago I dropped something on it, but it didn't seem to hurt it at the time. I guess it did. It's just about dead now.

Thanks for the advice. That's exactly what I did before I read your reply. I went to distilled water, 5.8ph, 480ppm. I'm using gh flora series and went with a 1/4 solution. The other plants have perked up nicely and aren't curling under anymore.