I’ve done both, in actuality whether it be nute burn, nute deficiency, or PH imbalance, starting with a clean slate should help any of them.
That’s why I threw out the fresh reservoir change.
I also mentioned the pumping of plenty of oxygen into the water because you can offset water temps, to a point, by adding more dissolved O². Any temps beyond about 78 degrees and it’s going to be difficult to pump enough oxygen in there to offset the rising water temps. If your roots are nice and white and there is no funny smells coming from your resovoir then you probably don’t have root rot.