I'm not there, but those don't look bad at all, they are pretty white, should be able to be saved . Those plants are young, probably shouldn't have messed with the roots, though. What EC were you running? They don't have many secondary roots so they shouldn't be on any nutes really, or extremely low EC. I've stated running just tap water until i see the secondary roots. What did the res smell like? An infected res will smell bad, it's hard to explain. The liquid karma stains roots brown, kinda looks like that. I thought I was getting root rot initially, then I figured out it was that stuff. My pumps usually have a thin slimy coating on them when I pull them out, but it might be the hydroguard colony, since I use it. I store my RO in a 55 gal drum like you, I bought the smallest air pump I could to keep it agitated. I opened if after about 8 months, thinking I should clean it and it was perfectly fine.
If your running h202 in anything organic, your fighting yourself. You either need to go full sterile, or run bennines. Only time h202/bleach should really need to be used is in extreme circumstances where you want to nuke everything, in my experience.
When you get the hydroguard, I'd run base nutes to .5-.6ec, liquid karma to get it up to .6-.7 Ec, and HG @ 1ml/L initially, that's it. After that, use the HG at 0.5ml/L. Once they start bouncing back get EC up around 1.0.