if the leaves are turning lighter green to yellow, you might have a nitrogen deficiency, which may be rectified by a simple compound comprised partly of your own urine. If you're using store-bought soil, there's usually enough nutrients to last 3 months. if it's cruder soil, you can add various things. the most important nutrients to the cannabis plant are nitrogen, phosphorous, and potassium. do searches with keywords like that combined with words like cannabis to get tips from pros.