Stem Rot?? Need some advice please!

I switched to 12/12 and added full bloom nutes. I realized that I accidently went a bit overboard on nutes, and started to get some root rot (temps got to 90 for a day or 2 after I changed to my HPS). I drained my res, and there was a bunch of salt on the bottom... I cleaned, flushed the plants, and refilled. Also added H2O2 and the roots are all nice and white again.. I ran plain water for a day, and then added the proper amount of nuts back. Most of the plants are doing good, but one had gotten some serious rot on the stem... If it is rot... Really not sure what it is! but the leaves are drying up and I was wondering if there is anything I can do, or if this plant is a lost cause... I also have another plant whith the start of a problem on the stem as well... I hope it will just recover, but pics on that one included as well....

My Setup:
6 plants (Bag seed) in a 13 gallon DWC drip system, and a 400W HPS. I have 1 extra plant in soil as well. I'm using GH Flora series, and have been in 12/12 for 6 days now.

Any help would be appreciated!!

thank you!

the 2 pics of the stems,those plants are toast,cant see them coming back.

Hey Trapper,

Thanks for the post... Yeah I pulled one last night.. The other one (second stem pic, or 3 rd pic) is my biggest plant... I really want to try and save it.... Is there anything I can do to help? it is nice and green under that spot... there is only about 1/2 in of where it is dried at the base of the stem.. Roots are growing better now too.. but I would appreciate any help on what I could do to save it....

thanks!