Please help!! Crop is dying fast

Hi, ive been growing for two years and i have never experienced anything like this before and cant figure out what to do. This is the 2nd run that has done this in a row but this time it is much worse.
1st off, im battling powdery mildew but keep it at bay with neem and soap every few days. Besides that, the plants appear super healthy throughout veg stage. As soon as they start to flower, things get ugly. At first we thought it was thrips and i was treating them with Monterey Pest chems. That seemed to help the first run make it to bud, although the yield was about a 1/4 of what it should have been. This run the problem is much more aggressive and i still have over 5 weeks of flower left. Essentially the plants look as though they are being over or underwatered but im pretty sure that is not the case, although I could be wrong. Also, the leaves are quickly yellowing (starts at tip but quickly takes out the whole leaf) which is quickly followed by a greyish color that takes over entirely. It almost looks like mold. I have enclosed pics.
This is a hydro setup with hydroton as medium.
I am using the botanicare line (pro grow/pro bloom with cal mag, sweet, karma, aquasheild and clearex at appropriate stages). I keep the ph between 5.7 and 6.2. And i monitor the ppms (1500 or less). In the pics you can see that one plant remains fairly healthy as all the rest are quickly dying. Any ideas? Its breaking my heart as this is supposed to be an awesome strain which unfortunately the name is escaping me right now. Please help!

try the hydro section mate, they will know. good luck

Is it old or new growth that is turning yellow ? Or just the whole plants

What's your humidity? Getting pm before getting to flower makes me think your humidity is too high. I used 1200 ppm in hydro, was pretty happy with it, but haven't used your brand before so its not really relevant.

Just saw the pics as well is your res in the room? And what about it's temp too?

Duh just seen pics, can't really see that good on my phone but it looks to me like the plants are rotting from excess water ?

It starts with the new growth but quickly works its way up to the middle and even some top leaves. The humidity is around 55 to 60 %. The reservoir is in the room (directly below). The temp. in the room is usually between 60-75 degrees depending on the temperature in the house as I do not have a totally climate controlled area. Would over watering cause the leaves to turn into that greyish brown? I'll check my watering cycle and get back to you on that. Thanks for all the replies guys

Over watering would, but you would smell it

ItsA process of elimination look sniff touch nothing should smell funky if it does change/remove it look for signsa of bacteria you have pm so its already there and finally touch you know what it should feel like

Water Saturation can do alot of damage, where are the plants that are unaffected check you water flows etc

Unless your solution is starved for oxygen you can't overwater in hydro. Are you doing dwc? Drip, ebb or what? I can't tell for sure but it looks like ebb or a drip from the pics.

I'm not sure what DWC is. It's the kind of system that the reservoir pumps the water into the upper tray that fills up all around the pots. I have to admit that I'm pretty much a novice. I have been fairly lucky in the past two years and only had to deal with spider mites and powdery mildew, which have been fairly easy to keep under control. The spider mites have been completely erradicated (at least I haven't seen signs of those in a long time) and the powdery mildew creeps up if I don't spray for more than a 6 days. I did come across this post in another forum that looks very similar to my issue. He talks about Thrips giving him a fungal issue.? And says he used T-22 and an inoculant. Here is the link to that forum http://www.uk420.com/boards/index.php?showtopic=101822&st=250
This may very well be the issue but his post is kinda vague and I am not sure if I should try it unless I am sure this is the issue. I am also afraid that the T22 will negate the Liquid Karma.

Alright, let's see the roots.

Yeah, I'm going to go ahead and pull the worst one out and "dissect" it. I'll post some picks in a few hours.
Thanks guys

I'm not a fan of hydroton in an ebb n flo, which is what you are using. I don't think it wicks up well enough IMO. Id go with some rockwool maybe next round. How often are you flooding? Not that it's your issue, just throwing thoughts out there. Trying to get a full grasp

Yeah, I'm going to pull the worst one out and "dissect" it. I'll post some pics in a few hours. Thanks guys

I;m gonna check the water cycle and get back to you. It might take me a little while as I don't like to use my home IP address for this. Thank you Free WIFI

Stay away from the %$# at your local "grow shop"...where they say more is better, to which should be said "less is more, its a fucking weed". I am in a area that has one of the worse spider mite problems in the us..without some magnification it would be easy to misdiagnose the problem..turns out the little white spots can be from too much neuts or certain forms of bacteria... if you have the luxary, try planting your favs in some quality top soil as a control group...not to mention the taste is .