Nitrogen to a Plant, is the same thing as Protein for a Human Being.
Humans eat protein, and the body converts it to Nitrogen.
According to tissue analysis, marijuana basically likes the SAME AMOUNT OF NITROGEN, AS IT DOES PHOSPHORUS, AND IT LIKES 2X THE AMOUNT OF potassium, AS IT DOES NITROGEN.
Magnesium is the #1 deficiency in container grown plants.
Marijuana is a HUGE consumer of Magnesium, and it needs it every feeding.
Also do not let your plants get so dry they droop. If you do, you will concentrate the salts, and when rehydrated WILL burn your plants, possibly cause PH imbalance, and lockout.
I have used a CHEAP Lowes ( or equivalent ) Moisture-PH-Light Meter for 40 years. I also go by the weight of the container, but the moisture meter lets me be more precise.
I NEVER let the needle get to DRY. always Low Moist.
Marijuana likes a 19.5-20-39, and then you adjust for PPM.
In an 8 weeks flowering strain, they should be given a Monopotassium Phosphate ( 0 -52-34 ) Boost from weeks 2.5- week 4, and weeks 5-6 need a Magnesium/Sulfur Boost. Weeks 6-7 the nutrients should be a bit less, but NEVER totally devoid of food. Closer to week 4 PPM, with No MPK boost.