Is this N def or Mg def?

Well it doesn't really look like a magnesium def, N yes. Those brown splotches are possibly some micro nutrients defs, I've seen calcium do this but normally it has a lot of spotting to go with it. Could be the ph slightly off (or swinging perhaps?), but your plants look great over all, if this is just on a few lower leaves I wouldn't worry too much. Looks like you are into 3 or 4 weeks flowering already so this stuff isn't too uncommon, especially if you switched nutes at 12/12.

Nice looking group of ladies there!

 

Some of my lower leaves are doing the same thing! i havent been able to pin point it yet!? They are gettin plenty N... but no Cal-Mag

 

check the soil looks like aphids or termite for aphids use malathion
not sure what to use for termites

 

That's a problem, definitely related to salts and pH imbalance. Some people will try to nail this issue down. I'm starting to wonder if it's related to using phosphoric acid pH down and creating precipitates. You seem to have purple stems (Mg), burning (P, Mn), leaf curling up (heat, K, Ca, Mg), yellowing (N, Fe). The necrosis between veins is bad, killer really.

These leaves are never going to heal, so when they are more than 50% dead you need to get them out of there. My thought here is that you're a few weeks into flowering, and you either added some kind of bloom supplement, or you're just feeding this strain too much at this stage. Around week 3 to 4 I find my plants need a lot less food than they did leading up to that point. Basically half as much. I used to make the mistake of thinking more is better during flowering when in fact I needed some potassium and calcium while relying on residuals in the media to feed the plant.

This is a complex problem though, and it's pulling from a variety of illnesses which makes it hard to diagnose. I've personally seen this in my garden so I am speaking from experience. I've tried the whole micro spectrum, and of course more food. Adding things to the system at this point can be a losing battle so here's my mentality on the cure.

Something is wrong with the media. It could be the pH. It could be mineral and salt related. It could be underfeeding or overfeeding.

Doesn't matter what the issue is! Because here is what you do for all of them:
Flush the media with Reverse Osmosis water with a pH reduced by citric acid (lemon juice) or by using ClearX (or similar product). Aim for a 6.5, and make 10 gallons of the stuff (two 5 gallon jugs).

Pour the water into the planter, 5 gallons over the course of 10 minutes (I know, really slowly), and then the last 5 gallons over the course of 5 minutes. Do this in a bath tub or something, and you'll see the water draining out start yellowish and eventually run clear for several gallons. Allow the plant to drain and rest for 12 hours.

Okay, so now you have a very wet, very blank slate. You don't want to starve your plant of nutrients, and you also need to take care of your organic root zone too. So mix up a normal strength feeding of nutrients. You want to make sure you are including things like n-p-k, cal-mag-iron, manganese, silicon, and humic acids. Feed your plants now while they are still wet. To avoid root rot allow at least 5 days to pass before even considering feeding again.

Now you have a cleaned and reconditioned medium. Whatever the old issue was should no longer be present. Flushing a plant can be a bit difficult but the end result is generally better than not.

I hope this helps and you don't do anything drastic. Help your plant now before you lose too much of the leaf mass.

 

Seems we are heading down the same direction, I plan to flush tomorrow, I think my problem is I havent flushed once this whole grow, and maybe switchin the nutes over its fuckin with it...

Good luck man, leach those snatches!