Plants Starting to die 3rd week.

Hey Guys,

ebb and flow
6x6 rockwool cubes
40 gal res
PH 5.5
PPM over 2000
RO water
watering three times a day for ten min while light is on.
Flush with ph water for a day at the end of each week.
Temp. lately 75 - 89 last week 98
Humidity 50

First off, this is the second time this happened... My veg is great, then around my 3rd week in flowering the weaker looking ones start to turn yellow and start to droop, and eventually die. It's like they just stop drinking water and there is no bringing them back. I have tried a bunch of different things. Like pulling them out of the water cycle and flushing them with just ph water. This last week the temp got really high and I noticed a lil heat stress on the tips, I don't think it is the temps because most of the my guys look really good. This is kinda why it has been so hard for me to figure out what is going on. I have been doing a bunch of research, I am thinking that it might be a nitrogen deficiency? They're also are getting purplish steams.

Whatever it is it mostly the weak ones that die off, then the others start to go...

Here are some pix of the bad ones. I did get a pic of the ones that died but they looked like third one but way more yellow.

Thanks!!!

They look hungry and thirsty for sure...

What do the roots look like? The vegetation might not be stressed by the heat, but the roots could be.
Is your water oxygenated enough? What is the res temp? Do the cubes dry out between watering. Looks like you are doing your research, you've probably already checked this stuff.

The fact that it has happened twice after flowering seems like a clue. Obviously the nute solution changes after flowering, but what other factors change about your grow room? More lights? Higher heat?

Yeah..

I don't think they are not getting enough water.. The cubes are very saturated, I almost think that they might be getting too much water. You think 3 times a day for 10 mins is too much?

I have been doing some more research, and I think I am watering too much, and maybe drowning my plants.. The 6X6 rockwool cubes are really heavy and have a lot of water in them. How wet should these cubes be?

Thanks!

Come on peeps.. What do you guys think?