Root rot life or death?

You could do applications of h202. I'm not sure how much per gallon and how often (probably daily), you'd have to search that up. But it will add oxygen to the water and kill just about all bacteria (beneficial or bad). You could also use a preventative, like hydroguard, slf-100, vodoo juice or some other bacillus bacteria product. Those products are designed to out compete the pythium so root rot doesn't happen. Root rot isn't a grow ender, but if you get it and you don't fix the temp issue, it will probably be difficult to manage.