I just feed the recommended dosage on the chart provided! Corey formulated the nutrients specifically for cannabis so you shouldn't have to worry to much about over/under feeding. You may need to adjust dosage's slightly depending on strains but for the most part the feeding schedule chart is pretty accurate! Don't be to afraid, cannabis can take quite a beating and these are quality nutrients that would compare with all the top hydro nutrient companies, just give it a try. If you are using the hydroponic synthetic line of BPN a TDS meter could help with more accurate feedings but it is not necessary.