hydroponic root rot problem

geez, no wonder, i just stuck the tops in a jar of water and changed the water every once in a while. no wonder it started growing root rot. ill go ahead and try the peroxide stuff and hopefully it will go away btw, how much do i put in?

edit: it worked! i put in a capful of it and it's gone by the morning! now i just have to figure out how much exactly and how often.