Hi mate, it will be easier if you have a TDS/PPM meter. With AN fertilizers and almost a full line of stimulants - I don't go beyond nutrient solution concentrations above 0.9EC for early veg, 1.2EC for the active veg stage, and 1.4-1.7EC for the flowering phase. The concentration of your nutrient solution, directly depends on the quality and power of the light flux. Just follow the manufacturer's chart, but divide their recommended concentrations by two. It is always better to underfeed than to run around with your head on fire and save your plants from an overdose)