Or your roots are sick as stated
.
I've come to my own conclusion through trial and error and reading many, many posts about root problems and they all seem to have a common factor, excessive EC. Over feeding provides extra food for bacteria, at the same time slowing the plants uptake(nute burn/ lockout), which can cause root die off, creating more food for bacteria. It's a vicious cycle. Everyone wants to start feeding their plants ASAP, when it's not usually needed, and generally too much.
Simply dropping ECs removes this excess food source, allows the plants to resume full potential, which in turn uptake more nutrients, relative to the stronger EC from before, removing even more food sources for root bacteria.
Keeping the res clean, ie: no dead leaves or excess dead root material and not providing a nutrient buffet for bacteria, along with bene bacteria dosing, have kept me root problem free for close to 2 years. And I regularly saw mid 70 res temps in the summer.
Ya gotta figure, there's outdoor commercial growers running DWC, RDWC, Dutch buckets, etc who's res's are @ambient outdoor temps and they don't lose everything to rot pathogens constantly.