Acceptable nutrient levels depend on the strain. I've seen plants that could take upwards of 1800-2000ppm in late flowering and love every bit; however, I've also seen some strains (blueberry especially) that can't take more than 900-1000.

Keep raising it slowly week after week and wait for the very tips of your leaves to get nute burn. Once they do, keep it there for a while or back it off a bit.... trial and error