What should my PPMs or ECs be at each stage of growth?

This really varies, because if you are growing in an accelerated environment, such as adding CO2, you can run much higher PPMs (meaning you can feed plants at much higher concentration rates.) The amount of nutrients plants can uptake also depends on their stage of growth, i.e. smaller plants need less food. See our nutrient calculator, or more information in our Hydro 101 section.