I'm going to disagree with my growmie here - simply because phosphorus deficiencies start on the oldest leaves and move upward - and I don't think this is the way it's progressed on your plant?
I saw your question a couple of days ago and I honestly did not see anything wrong... but NOW, with THESE photos, I can clearly see that there IS an issue. First, let me tell what it's NOT... it's NOT wind damage or water damage or light or heat damage... but I'm not sure it's got something to do with your nutes, either. I'm wondering if it's some kind of fungus... so I'm going to ask - if you rub those spots, does it smear or come off on your finger? Or is it dry/brittle to the touch? If it smears or comes off on your fingers, it's going to be a fungus... if it's dry or brittle at all, it will indeed be a nute problem and probably a calcium/magnesium deficiency although that would show a yellowing to the leaves as well. A fungus will be the worst diagnosis... it comes from humid conditions and can only be solved by using a fungicide... in the case of SOME fungi, you would probably have to pitch the plant and thoroughly clean the entire tent but you should do research to try to identify exactly WHAT fungus it is..... I literally have no idea. If it is a calcium/magnesium issue, just adding cal/mag to your nute program should help if you're not already supplying it.
Good luck... and don't hesitate to come back if you try something and it STILL doesn't work... we're here to try our best to help!