How dark is too dark?

You're on the hairy edge of a nitrogen toxicity - I would cut back the Vegan Mix to 4tsp and the Bio Live in half to 1.5tsp (this has the MOST nitrogen in it!). Other than that, the grow looks really good - but if you don't get the nitrogen cut back, you could be seeing deficiencies pop up as nitrogen toxicity has the nasty habit of locking out other nutrients. When you get to flowering stage, I'd cut back the nitrogen even further but not cut it out completely... Nice to see you using Langbeinite... that should actually help you avoid any calcium/magnesium deficiency! Good luck!