Sorry, never used a hortilux light so don't know much about it. Use NPK fert with high conc of P for flowering. Use no more than recomended amounts on packet, I find it works better to give half the recommended strength twice as often, If your growing hydro, I don't know (I grow soil only). To flush, put your plants in the bath and turn the shower on warm/cool. Flush water through the soil untill liquid coming out of the bottom is almost clear, hence the name 'flushing'. Hope I've helped