leaves have spots

I was about to start flowering my plants, but it looks like I have a phosphorus deficiency. Does this seem like the culprit? The plants are about 4 weeks old, and there are only a couple leaves like this, nearly all of them are at the base of the plant. My nutrients have an npk of 5-3-3, but it has no instructions on how much to dose, so i just give my plants a very small amount. If i have nutrient deficiencies, what nute brand would you suggest i buy, and should i be concerned about adding too much nitrogen just before flowering?

that is calcium def

youll need some calmag

P def would be would be the least likely problem in a soil grow

a safe appropriate dose of your 5-3-3 would be 8 to 10mls per gallon (even during bloom)

add 5mls per gallon of calmag and 1/4 tsp per gallon Epsom salt

later in bloom (maybe 4 wees into 12/12) you might need a bloom booster to up your P and K slightly