Ok, Got a pic for anyone to troubleshoot. This is 3 weeks old. It's growth seems to be stunted. I changed my res with fresh water and used flora series for the nutes. The mixture is followed as indicated for seedlings.
1/4 tsp per gal of all three. PPM shows around 640. Help Please

PPM 640
PH 5.0 - 5.5
Watering every 12 hours