Sour blues by mephisto. Day 42. In promix HP. Tangs feeding schedule with some added pk boost. Temps around70-78 rh 35-48. Using straight RO water with calimagic added for cal/mag at 2ml per liter. I've tried upping their with no signed off improvement or hardly any. Should I flush good and start over? Here's pics. Over needed help for awhile but didn't want to bother any one. The real bad plant has been like that and losing leaves for over a week now. I should have called for help sooner I'm sorry. @Waira
that's some nasty lookin' leafage there mate! Advanced symptoms can be tougher to pin down, but other less affected leaves may be more clear, and where on the plant it happening worst... looks like it at or near the tops of colas in this case, so I'm thinking Ca defc. (poorly mobile nute element); P defc. can look similar, and on occasion I think it can affect higher, but if you dropped high PK at least a few days ago, and symptoms are progressing on even lesser affected leaves, P defc. is likely out,.. more hammered leaves may still crap put regardless, basically the plant is cutting it's losses on such damaged leaves and dropping them. Plus, you're using RO water, so there's no CaCO3 input from there, and 2ml/L CaliMagic is a low dose, apparently leaving you short on Ca,.... Any idea what the pH is? barring bad pH, no flush called for on this, just upping the Ca-Mg... I know CaliMag' is 1-0-0, but that shouldn't be an issue...some Ca-Mg product, from AN(?), I heard was 4-0-0, and that would be a problem in bloom like you are! Alas, this also means a foliar spray is risky, but if you sniper-shoot the spray, avoid buds as best as you can, get the leaf undersides especially, and use a proper water spreader/wetting agent, you can speed delivery a lot,... just make sure she's out of direct light until dry, and dry by lights out to avoid potential mold issues! 
nothing doing mate, I have no way of being certain about many diagnoses,...diagnostics are a bitch! so many things can get tangled into the equation, so to speak,..some symptoms are overlapping across some defc.'s, which makes it all the harder at times-- I advise as best as I can interpret! But thank you for the kinds words regardless my friend
..... So, wait, you say the lower leaves on the others are more affected than the uppers? Hmm, well Ca can show there too, usually around mid-cola, but this is just a generalization, not a hard and set rule,... And you say, this all started before you added the PK booster, right? The other, more remote possibility was K toxicity, which can block Ca uptake, but you have no edge/tip burn, so I ruled that out,... that, and the 0-15-15 isn't that fierce, not like gonad blasting stuff from Fox Farms or Hawaiian Bud, which have huuuge PK values! 
... Go full power on the Ca-Mg, ASAP,.. foliar is just another treatment option, but in-medium dosing a must,.... Oh-- pH? Did you score an Accurate 8 unit yet? That helps so much, and so much better than the damn run-off test... If you're in Europe, it may not be available under that brand name, but there's identical unit rebranded over there,.. never got the name though, but if you look it up (Control Wizard is the co. name) you'll see it's the same thing, nothing else looks like it,... 
hsoil: (short probe is the A7 model here)
