2 seedlings dead already please help

I have these seedlings In a toe style ebb and flud with ro water mixked w about 15 percent of the lucas formula not sure what's going on already have had 2 seedlings die please help...i keep the ph between 5.5 and 6.5...im flooding about every 8 hours for 5 min......

Lose the foil..it makes hot spots. White paint is better. Too eatly for nutes. Its burned.