First Grow - Triple Automatic: Purple Haze, Apple Fritter, Purple CousKush

Week 2 it is. Not sure if they are doing really good, but they grow. Second set of leafs out, first real leaf about to build I guess (?). Unsure with the light, should I still go with ~200-300PPFD as recommended for seedling stage, or rather up to 400-500ish for early growth? Since they don't seem to stretch to much, I'm going with a couple of more days with around 300. Since I have no dimmer on my light it is more around 330 to 350, depending on where I measure. Watered a bit on Day 11 to keep humidy around 70% because the first 1.5inches/5cm were really dry, around 400-500ml per plant. The leafs seem slightly yellowy, not so dark green. Could be a bit nutrient burn because I likely chose not the ideal substrate (Plagron Grow Mix, rather strong pre-fertilized. It's supposed to be enough fertilizer in there for the first 3 weeks of veg)?