An example: I use a PPM meter on my water. It's about 450ppm to start with, to which I add about 300ppm of fertilizer. So the background crap is more abundant than the fertilizer!iann wrote: Strangely, hard water can be packed with far more minerals than you'd dream of adding as fertiliser, but no problems.
For comparison, 1200-1500 ppm is about the concentration of fertilizer in a hydroponic system.