If that's coco, you should be feeding already. I start my seeds in a 300ppm (0.6ec) nute mix just to keep the coco's CEC happy. Once you get a few nodes, or they show signs of being hungry, you can start upping the ec.
Nutes at this stage are basically for the coco. Keep it at 0.4 - 0.6 ec and you won't burn the little youngsters.