Drooping leaves, no idea what's wrong

Two days ago I got my young girl on her first feeding cycle in my dwc/bubbleponic system. Adjusted the pH to 5.5 (the same as the clean water bath she was in prior to feeding) and added ferts to 1/4 strength as I normally do for the first feeding or two. Last night I noticed some drooping all over the plant, so I readjusted the air line (waiting on new air stones) as it may have not been in the water overnight.

Today I go to check on her and a leaf that was drooping moreso than the others showed some discoloration. The plant itself is looking a bit more lively today though. Roots are still pristine white as well.

I have three thoughts:
1. I didn't burn off enough chlorine (although I have 3 seedlings in the same water that are doing fine)
2. Lack of oxygen in the reservoir
3. I over fed

Pictures are included, please help me figure this out.

First pic was before the feeding, second is of the plant (still drooping, but looking better), and the third is of the damaged leaf

Bumping for assistance

I know most about soil so I am just going to follow and add, to your list: 4, PH and 5, water temp then to change to another food. Assuming also that the water level is right.

pH was adjusted to 5.5, water temp is floating around 72f. Roots are completely submerged, and my ppm is 1/4 total strength (at work and can't remember the exact number), but I'm using technaflora nutes.

I've been growing this strain for about a year now following the same routine as above, and have never had this issue.

Thanks for the input though!

Another picture update.

I emptied and cleaned the reservoir, refilled it, recalibrated my meter and adjusted the pH to 5.6. No nutes for a few days at least.

I also went up and disinfected the entire room.

The roots are stained a bit from my nutes, but they definitely don't look healthy anymore (no pictures of those at the moment). They still look and act alive, but they aren't happy.

I'm soaking the roots overnight in highly aerated clean water in the freshly cleaned reservoir and giving her a little darkness to recoop in.

Added a picture of the damaged lower fan leaves. New growth is very dark green ... Maybe too much nitrogen in the last feeding? A touch of burn on one of the new growths I just noticed and grabbed a picture of.

No clue what fixed it (cleaning and changing the reservoir, dropping the nutes out for now or what) but she's regaining turgor pressure and is starting to look good again .. Minus the damage already dealt of course.

If anyone could point me to where I screwed up, I'd still appreciate it

Are you using anything to keep the rez clean/sterile. If you're organic something like hygrozyme. If sterile bleach, pool shock, h2o2 will all work, some better than others. Look into different options to see what's best for your situation. DWC and root rot seem to go hand in hand. The warmer the solution in your rez the less o2 it holds, the easier it is for Pythium to take hold.

I've been running h2o2 (i think I'm going to up the loading a bit), and I'm looking into a homemade water cooler to keep the water at a consistent temp .. I'm wondering if the heat from these last few warm days may have affected the res temps during lights on