everything is going wrong, but no changes!! What is it?

I haven't changed anything, but suddenly my flowering plants, 2 weeks in are losing the fan leaves (although the buds seem to be growing). The leaves are turning yellow and then dying/falling off.
Worse, my veg babies completely wilted yesterday. They look like they haven't had any water, but I just changed the water - it isn't too warm, the humidity is about 50%, as always, the temps about 85-90. ALL my plants, in both rooms, have some black roots.
PLEASE help with anything you can. Any advice? This is my first time growing. I can't figure out what possibly could have happened.
I'm using Fox Farms Grow Big in both, and both Big Bloom and Tiger Bloom in the flowering plants. I use reverse osmosis water only. PPM is about 650 in both. I have read that they should be higher in the flowering plants, but I don't know what more to give them.
I've attached pix. These were taken 2 days apart.
PLEASE HELP!!???

i meant to answer this question yesterday but something with posting wouldnt aloow me, first lets get to the flowering plants, you said they are flowerin 2 weeks in yes? did you switch nutrients to bloom the day you changed to 12/12? if so this is the main cause of yellowing leaves and having them fall off, this happens to many and happened to me early on, you are not technically flowering until you see actual bud sites, if you changed to bloom nutes 2 weeks ago you are prematurly depriving the plant of much needed nitrogen, when we no longer need such high amount of nitrogen, its usually after we see flowers, to fix this issue in the future you need to feed bloome nutes after you see flowers, so by the time leaves yellow and fall off, you should be around 5-6weeks into flowering, this is totally naturual, hopefully if its an 8 week strain most leaves would fall off by the time harvest comes, this is good, leaves falling off too early is not good, you cant get the most out of the plant like this, lets get onto the next part

i can onkly assume when you say the roots are black you have root rot. is it brown and slimey and the water smells like a sewer? with air temps at 85-90 i would believe this is the case, the plants look like they need water yet they are sitting in water, what happens is the pythium(root rot) covers your root system and chokes out the roots, basically intercepting any water and nutrients your plant would normally get. if you cant control environment temps then no hydro for you, seriously, the water temp is ideal at 65-68 but anything under 74F will do....if room temps are 85 your water most likely is no lower than 83...this will kill your plants every time....i would try to help you correct this root issue but its a useless battle that will get expenisive until you can get an a/c in that room, now if your flowering plants have the stuff on the roots and you want to try to save your plants, you can grab the plant, run the roots under the faucet cold water, try to get all the stuff off as best as you can, get a spray bottle and mix 3% peroxide and water at 2 table spoons per gallon, spray the root with the mix and clean out your system with peroxide and hot water, then run only fresh water and peroxide 3 teaspoons per gallon for a couple days and repeat...i use hygrozyme its pricey but it eats up any infected roots, buts its $50 a quart, and i dont think you should invest in it until you get your temps down

I agree with morris 100%

the sad thing is, there people who run a 1000watt hps above the system and never have water temp issues, never seen root rot and nkow nothing of it, just flawless harvesting, dont that suck? personally, i would leave the temps alone at 90F, get a co2 tank setup, and a water chiller, but i see your in a cab and none of this is feasable....your running floros, whats your ventilation situation like?

Thank you so, SO much for your help! I'm beside myself. So, I lost the whole batch of veg phase plants, and I'm sure it was water temperature. The setup I have just isn't going to work. I am going to have to only grow one phase at a time.
The roots have some dark brown spots, but they aren't totally black and the water doesn't smell bad, so I'm hoping that I won't lose them. WE took them out to rinse them like you said, and they just didn't look as bad in the light as they did in the tub.
Yes, I switched to bloom nutes when I went to 12/12. Duh... Thanks for the tips on the flowering. I have read and watched videos and read some more to learn how to do this, and my info on flowering was sketchy. Our grow room is a large walk-in closet. We installed an exhaust fan in the closet, and we run it 24/7. We live in the desert, so we run either swamp cooler all the time until it gets humid outside, then we will switch to A/C. We run fans into the grow room to keep the sir circulating. It usually stays about 85º in there. With that light burning, and our outside temps so high, we just can't keep that room any cooler. I might consider a small standing air conditioner, but I'm so deeply inve$ted now that I'm hesitant.
We have floros in a box in the room, and are running 650 hps on the flowering plants. We have moved the floros out and are hoping to save two of the six. The indica all died first, so I'm sure it was heat stress. Our hydro store guys told us that here, you pretty much need water cooled hydro to use it in summer. We may harvest this batch adn then wait til Winter to start more. We'll just have to time our harvests so we don't grow in summer. My electric bill -- well, I don't even want to tell you how out of the ballpark it was last month. Let's just say it DOUBLED.
Thanks for the advice. I hope someone else starting to flower reads this.

you know this happened to me when i first went to hydro, happens all the time, i know you got plenty of cash invested into this, theres 2 ways, one you can scrap the whole thing and say it isnt for you, or two-add a few more dollars and MAKE IT GOD DAMMIT! since temps get so high, you may want to look into a water chiller, around $400 but it will allow you to grow like a champ and protect your investment, or you can go soil, with your situation you can get away with it, in many cases you need a chiller and an a/c, i put holes in walls whereever i go, so you know my smallest closets have 5,000btu a/c's - $90 from home depot...so there are options for you, its only prohibitive if your tight on cash and once you get a single little harvest you will wind up upgrading, whats the dimensions of the closet?

The closet is about 5' X 7'. We had constructed a box covered with tarp and hung floros in it, then used the outside to hang the hps. However, having to cover the box proved to be a bad idea. We installed a squirrel cage fan in it to circulate air, but it was big enough to exhaust an entire room, and was too much - it sucked all the humidity out of the box and killed the clones. And it made the walls rattle!
Since we moved the plants out of the box, and repositioned the flowering ladies, the temps have remained about 85º, but the water temps are cooler than the room temperature. All our babies dies from heat, and we have three large flowering plants that are very scrawny. Most of their fan leaves have died, and there is just buds all over the plant. It looks like Charlie Brown's marijuana plant might look, should he turn stoner. We won't get the yield we would have gotten out of it, but the buds do seem to be growing. We are leaving for New York for two weeks, and have an inexperienced grower looking in on the system, so cross your fingers for us, and I'll return to let you know what happened.
Meanwhile, to anyone reading this - DO NOT quit giving your plants grow nutes when you want to flower. I can't believe I made such a dumb mistake.
On the upside, we planted some purple nepal early, and put it in a friend's yard, and it's flowered and almost ready to harvest. So we'll have pot while we figure out what to do next. Probably try cloning until the weather cools off, then put in another batch of hydro. I'm not ready to give up yet, dammit!

do you have dark roots? if the water is under 75F(the point inwhich root rot sets in) then you should be fine, they can tolerate 85F, if they roots are infact covered in dark slime the plant will apear as if it is under watered or suffering from heat stress, looking all droopy, that slime if you have it blocks out water and nutrients from roots uptake, so it just may not be air temps killing the plants, also for the clones yes they love humidty, even 90%