Diy nft system, advanced nutrients

Running a DIY downspout nft system. 100 % Ro water starting at 0ppm. About 2 Plants a week keep dieing. Using advanced connoisseur line. Thinking it's root rot. But is there anything in particular that I need to nutrients. I read I need calmag. Suggestions.
Temp 76
Ph. 5.8
 
Top