dwc problems..PLEASE HELP ME..DESPERATE..

Hey guys, I posted this yesterday but I can't find my post... so I'm putting it up again...
Yesterday I changed my water in my multiple dwc
No more than 5 hours later 2 of my plants started looking a bit sad and drooping over. The stems have gone all soft and limp. The whole plant is just drooping. Within 6 hours I lost 2 leafs that went all dry and curled up..
My girl are 5 weeks old and until now they have been flawless... with spectacular growth and strength. Ive topped 1 plant and it responded really well. I've literally had no problems... I've done 1 water change so far and not had this problem.. my nutes are grow micro bloom ph perfect and I'm using 4ml Per litre as the bottle says. Ph is just that at a perfect 5.8 water temp is about 19c rh is 55-60 and ambient temps are 28c the strain of the ones having trouble are Blue cheese fem. I'll put up some before and afters

Please if anybody knows what could be happening or have experience the same this g please help out a very lonely grower.
I've searched and searched and have found nothing remote to my situation.. any help is much appreciated....

Something's not right with the new water you added, but I have no idea what.

Maybe try changing the water again?

How are your roots?

how is your water temp,looks a bit like cold shock to me

it looks like their not taking up water. definitely check roots for signs of root rot and the stem for rot. if its rot- your toast. make sure your meter is calibrated correctly then try flushing and using just ph'd water without nutes for 24 hrs and see what happens. good luck

OK turns out it was a water quality problems..
I brought some boxed spring water and changed it again this time with no nutes just yet. Within 20 Mins they started perking back up.. I cut off the dead leafs and tidied her up a bit and this is what she looks like now...

Just want to say thanks to all who helped. Seems 1 of my girls doesn't like the tap water here at all.... it's been over night now and she is absolutely perfect again..
Again thank-you.