During the first half of the vegging cycle, they'll want water with a ppm of 350-700 (EC 0.7 – 1.4). During the second half of the vegging cycle, aim for 700-1000ppm (EC 1.4 – 2.0). During the first half of flowering, increase to 1000-1250ppm (EC 2.0 – 2.5).