pH and EC are important - especially at the seedling stage.
EC, CF and PPM (of TDS) are, confusingly, different scales for measuring essentially the same thing.
EC (Electrical Conductivity) and CF (Conductivity Factor)
EC 1,0 = CF 10
EC 1,0 - PPM 500
EC x 10 = CF
EC x 500 = PPM
CF x 50 = PPM...