help need experienced grower's help please!!!

I am new to hydroponics. I am using a aeroponic turbogarden. I have had the ph set between 5.8 - 6.2 consintantly. I had the ppm at around 600 but I recently changed it to 1100 because I figured they had a N deficientcy.

My plants are growing really slow, are yellow, lower leaves have brown spots and are curling. What color are roots suppose to be? Mine are brown/white. I don't think my garden has a heat problem so I can't figure out what is wrong.