a good rule of thumb with most nutes is start off half strength, and work from there. its also dependant on the strain you're growing, i've had a lemon kush, a jack herer, and a sour diesel growing at the same time and had to feed them all different strength, the sour d took 900 ppm, jack would burn at 900 and only took 800, lemon kush only wanted about 650 before tips started to fry. also are those people talking about ppm using the same medium you are? soil and coco take less ppm than hydro, you can run over 1k ppm in hydro most of the time. over 1k ppm consistently in soil or coco will fry your shit like an egg