Brown Spots Crispy Dry Leaves

[geko26]

I have 2 Pineapple Express Autos right now under 24/0 cycle. Both soil, 400hps, light is about 1.5 feet from tops of plants, RH of 60, temps 75-80. Intake and exhaust system w/ carbon filter. FFOF is my soil mix. I use FoxFarm organic nutes (GrowBig and TigerBloom). I've read articles about FFOF mixes being hot, but I've never had this prob before in several of my past grows with it, from the same bag of soil, sooooo need a little help here. They're both about 4-5 weeks old, just starting to bloom. One of them is 100% healthy, couldn't look better. The other is very stringy looking and you can tell its yield is already starting to be impacted. The problem started maybe 2nd or 3rd week i noticed a little bit of yellowing on the leaves, i didn't worry much thinking it might've been PH fluctuations or something. But then brown spots starting creeping up. I've flushed the affected girl a week ago but I still see the problem creeping up towards the newer growth. I gave her nutes of about 400 TDS, every other feeding, about 3-4 days apart. After I flushed I didnt give nutes for a week. Still don't think she's getting any better. Not sure what else to try here. My PH is usually around 6.5, I've never tested the runoff for this one, but again I flushed a week ago and still don't think it helped. The problem started with the leaf tips on the lower leaves and worked its way up towards the top at this point. The leaves curl down, yellow, then start getting brown spots, turn dry and crispy. The stems are not purple or anything, they're green and healthy.

Any ideas?

 

[geko26]

Also, I hit her with a very small dose of cal-mg thinking it was a calc deficiency right after the flush. Some newer growth looks like it might be ok, but I still think it's getting worse. If you all think its def cal-mg deficiency with maybe PH probs compounding the problem, then I guess that's all I needed to know, unless you think there's anything else going on too. Should I continue to give cal-mg with nutes until I see green healthy leaves and am confident theres no more problem? The problem is affecting maybe 70% of the leaves right now. I know her yield is already affected, but I dont want to chop her, some is better than none, so should I continue to nurse and hold out to get what I can, or is it a complete waste? Only have 6-8 weeks left.

 

[hexthat]

how about a picture of the whole plant?

 

[geko26]

how about a picture of the whole plant?

Here it is. It looks better in these pictures than it actually is, as the majority of the green looking leaves have brown spots starting on the tips. The very newest growth actually looks ok, no spots yet, so maybe the flush and splash of cal-mg helped, but just want to make sure. It also looks a little skinny as there was some stretching early on due my lights being too high. I have a picture of both of them side by side so you can see how one looks full and healthy, and the other is much skinnier. Both are same strain, from same pack.

 

[hexthat]

IMO it need more phosphorus but ehh

 

[spartacus420]

Phosphorus deficiency...

flush with ph'd water