2 to 3 weeks from harvest. Yellow leaves up top. What is this?

Im on my 6th week on a 8-9 week strain. The plant has shown some sign of nute burn plus some deficiencies, what is this and what do I do?

I have flushed the plant with 6.0ph water 4 days I ago. I am now feeding it nutes with some extra calmag at about 800ppm(0.5) at 6.4ph twice a day since I suspect this is magnesium def and I'm hoping increasing my PH to 6.4 from my normal 5.5ph will help with my magnesium uptake, but is this really Magnesium deficiency?

My current grow is linked on my sig. Thanks in advance!!

Looks pretty good. Personally I wouldn't worry about it to much, if you only have 3 weeks left. I mean leaves start to turn yellow once you get to the end of the plants cycle anyway, but I would think that it is a the beginning of a nitrogen deficiency.

Most plants do that somewhat toward the end. Doesn't necessarily mean N deficiency....

Because Man those are dark green and have obviously had lots of N.

So what do I do?

I wouldn't worry about it. It will be alright.

I'd give her water only from here on out. Probably a nute lock out from too much fertilizer but doesn't really matter at this point.