Hi there.. first i think that EC 1.1 is already quite high for a plant in that stage, but of course there are more influences like the environment, the intensity of the lamp and especially growth-rate that can change the requirements. Is the run-off the same as what you put in (or did i misunderstand the word "autofertigated"?)?
Odds are, that it's genetics though, especially when the other plant is showing no issue in the same environment. Then again, different strains have different environmental preferences, like warmth and so on.
In either way, that's an interesting setup you have there.
happy growing!