marijuana plant leaves browning/rusting (what is wrong?)

Hi guys my plant leaves in some areas are turning brown / rusting. Not just in one area of the plant a little at the top and middle and bottom. Can you tell me by the pic what this is?

thanks

how are the roots? are they in pots?

Looks like a Phosphorus deficiency to me. Are your stems turning a purple/red? Starting to turn downward? If so... may be a P problem. What medium are you growing in?

I just did a ph test today and i found out my phosphorus was at 7.0 which is normal and my nitrogen was at 5.7 and my potassium was at 5.7. So I went out and got a fert that is lower in P and higher in N and K but I am only going to use this for a couple of days so I can get the other 2 numbers at 6.5 and then I am going to switch back to my original 15-30-15. Do you think what I am doing is going to help?

obijwon that bug on your post triped me the fuck out dude haha!! I thought it was in my computer screen.