For more information, visit: br As discussed in lessons four and five, pay close attention to your ph levels. Your marijuana plants are looking for ph levels ranging from 5.6 to 5.8 during vegetative growth and 6.0 to 6.2 during flowering. Check back to lessons four and five for a more detailed account of reading ph levels and manipulating them.br br The unit measurement parts per million, or PPM, is the best way to determine what the concentration of elements in your water is. PPM meters are commonplace and can be purchased at your local gardening center. In regular tap water, PPM ranges from 50 to 150 PPM. The cannabis grower will want anywhere from 600 to 1600 PM for their plants depending upon the stage of the plants lifecycle. As the plants get older and grow larger, you should increase the PPM. Of course, this also means that during vegetative growth you should have a lower PPM than during flowering.