I have a serious problem... leaves turning yellow ...

cbalderson 60 man wtf are you talking about??? boron deficiency’??? have you ever seen one? no you didnt because it doesn’t occur that often..this is simple nitrogen deficiency and it’s visible from the airplane.. next time before you again post a copy/paste article from rqs about boron deficiencies maybe think about what your doing..

With a boron deficiency, upper cannabis leaves display abnormal and/or slowed growth. Growing tips may not grow properly, may display twisted growth, and may die off. New leaves may wrinkle or curl. Boron deficiencies are more likely to appear when a plant is underwatered or experiencing very low humidity (very dry air). Now for the yellowing I don't see any nitrogen are u using a grow nutrient for that or are you grow in a live soil/supersoil. If you are using synthetic pH in live soil/super soil your killing your microbes. But if your adding grow it needs some more and always pH at 6 to 7 in soil every time it's crucial.