Do as you wish. There is a science to growing plants. You post with a headline saying this is your 3rd grow and same problems, yet now you mention in your post that humidity is ALWAYS at 20-30% and it never caused you problems? Seems you're contradicting yourself, but it seems you know alot, so i will leave you be, good luck...btw, this is marijuana, not a cactus...15-20% humidity will cause you problems all the time! You're using rich soil, and feeding half strength...with such low humidity, the plant is sucking up too much water, too fast..the transpiration is not normal, and since your medium isn't dialed in, the plant will suffer, good luck!