That's popular, but not really necessary. If using pure water (low PPM) because the tap water is high in PPMs, just add enough tap to the pure water to get a starting 150ppm. There could be rare conditions where the tap water's minerals are so imbalanced that it wouldn't be suitable even to provide those base 150ppm. At that point, just use epsom salt and gypsum to replace some minerals.You wanna add calmag when using bottled or distilled water.