Crispy Brittle Leaves + More!

Chopping her down very soon, but Im curious what could do this over 2 days. I thought for sure that it was heat due to a heater being some-what close, but it has always been there and doesn't run very often or long. The entire plant seems to be effected, while other plants next to/nearby are uneffected entirely. Nothings been altered in her nute water. The first few of are the problem plant, the last 2 are of the plant beside her. My first real grow in my space. The 1000W HPS is actually quite far away as well, 24"+ inches away. Leaves are very brittle, they just crumble where they are 'burnt'

The last 3 are of my Red Dragon mother plant, all the older leaves seem to be showing the same signs, everything else looks mint, old leaves turn yellow, and brown along the insides of the blades. She's in 70/30 Coco/Perlite, 3gal. Run off is showing 5.8pH. At first I thought it was a cal/mag issue, so I doubled up with it for a couple waterings. A friend told me he had a similar issue and thought it was salt toxicity, so I've started flushing with 5.8 RO water. Plan on transplanting her soon as she is quickly turning into a monster but I would like to clear up this issue first!

Thanks for any advice in advance, my first grow(s), while I have read a lot, I am still learning..

 

Thanks for the compliments, but any idea what could be going on with my mother plant? Im leaning towards the salt toxicity as I flushed with 6 gallons of water with low PPM, like 80s~, earlier today, and after 4 were ran through, some I was still seeing 600+ PPM.. I made the mistake of not taking an initial reading, but I ran 6 through her today, and I cut some clones.. Going to let her dry up some and run some more water through her.. But if anyone has any other ideas, send em' this way. I find it hard to believe its a deficiency, or lock out. Run off has been 5.8pH solid for weeks after an issue with that, and I tend to be quite heavy with my CNS17, Cal/Mag.

 

Working on it still, have had limited opportunity to fix the issue the past couple days, I'll let you know when I've corrected the problem.. It's been ongoing and a royal pain in the ass.

 

So I've flushed twice now and let my mother Red Dragon dry up, and gave her some plain water Im wondering if being rootbound can cause complications like this over the past week or so.. Leaves are still browning. As they yellow they become very brittle. pH run off is still between 5.7-6.0... She's massive, and only in a 3gallon square pot. Her leaves don't seem to darken up any either, while she was younger, her leaves were a very healthy dark green.. Now they've seemed to become lighter, as well as the old growth still yellowing, brittle, and then finally turning crispy brown.

Other than being rootbound, I did have spider mites, which were wiped out, and then reintroduced again (thanks to dumb friends). However, DoktorDoom kept them more than undercontrol, we're talking extremely minor stuff here, mites haven't been able to cause ANY plant damage. However, I'm wondering if the Pyrethum, although such a small amount in DoktorDoom, could cause lasting effects on plants.. Possibly similar to this..

This has become a major headache trying to keep her in check, help save my mother!

 

Sorry, I think some people are getting confused here. The flowering pics are no longer an issue, as they have been harvested. The problem remaining is the mother plant. The root pictures are of the harvested plant. The last 3 pictures, the individual leaves, are pictures of the problem plant (mother Red Dragon).. She's not being cut down... because she's not even flowering..

So to clear up any confusion, here are the pictures and problems again.

My mother Red Dragon plant is in a 3 gallon 70/30 Coco/Perlite mix. She's about 3 1/2' tall, LST'd all over the place, into basically a 3 1/2' x 4' x 4' cube. Spider mites have been a very minor some-what ongoing problem in my garden, once it becomes warm enough, everything will be getting dumped outdoors, and the room sterlized and replanted with new unaffected plants. However, the problem remains.. She has yellowing older leaves, which turn very brittle and then brown. Foliage has become a bit lighter green, but I believe this is due to 2 flushing and plain water only waterings for the past week. Before flushing, pH was 5.8. Lock out wasn't an issue. After flushing pH is still 5.8, PPMs are low 200s now, the water I was using was about 115PPM tap water. I am going to slowly give her more nutrients now as I don't know what else to do and I don't want to starve her. She's a few months old, and has been growing like crazy despite these problems under a 1000w MH. But I fear if I can't control the problem soon that I will just junk her and start fresh. Reincluding pictures. Keep in mind these leaves go from what you can see in the picture, to completely brown and curled, and just crumble. More pictures of the leave are in the original post above