would add more nitrogen and P / K 131?

Yes add just a little NPK however this is not your problem. Read the labels of what you have been feeding them. My guess and definite answer would be your plant and nutrients are lacking many of the micro nutrients which is the bottom tier and least used. However greatly needed especially when going into flower. The yellowing all around your plant is definitely a sulfur deficiency. A lack of nitrogen will also yellow the plant but only beginning at the bottom of the plant and working it's way up, that's why NPK and magnesium are called mobile nutrients they are stored in the oldest most lower leaves until needed. That's why you always want to ensure that they and only the older low leaves are nice and darker green. While the top portion or new growth overall are light green to a normal green. Secondly since the yellowing is also occurring from the veins outward this is a iron deficiency as well. And lastly your leaf tips are curling, this is a definite sign of a copper deficiency. All these are easily fixed, with a mirco nutrient supplement. You should be able to find one pretty easily. However this will neve be a issue again if you go organic and use mycholrizal fungi and trichoderma bacteria blend of some kind. Like Recharge or Great White for instance in combination with Espoma garden tone which contains 7 different bacteria that work in tandem with the mycholrizal fungi and trichoderma bacteria to deliver your plants the nutrients they needs. Only when they need it as they form a symbiotic relationship with the plant. I suggest you invest in these organic grow materials. But for now you need some micronutrient supplements for the time being since you're in flower already.