John_Thai Yes, if you haven't added nutrients, it's time!! But I never add as much as they recommend, especially when a plant is young. I start out at around 25-30% of what they recommend.
And I keep a close eye on the leaf tips to look for nutrient burn. http://www.growweedeasy.com/nutrient-burn-cannabis
AND I just give them 24 hours of plain pH water about once a month just to clean excess salts/minerals out of the plant's system. This way seems to work very well to keeping the leaves looking nice and healthy, and for vigorous growth. ps. YOUR ENGLISH IS GREAT!!!