Athosanswered grow question 6 years ago The plant does not seems to be stretching so I don't think it's a light distance issue. 250 PPM is fine for a seedling, but now your pant is leaving seedling stage and entering full vegetative growth, so it's starting to demand a bit more nutrients. Ramp it up slowly, 350 PPM sounds fine, you can always feed a stronger solution later if it's not enough.
Don't start bloom nutes yet, the first part of the flowering stage, the stretch needs grow nutes, I would switch to bloom nutes in 2 weeks when the stretch slows down.