You may already have root rot if your rez temps have been high.
If your roots are slimy then you need to combat the root rot with some h202 and enzymes.
Then you need to make sure the temp of your rez is 68º or lower,
so the solution will hold enough oxygen to prevent the root rot from returning.
If you cannot get the temp down then you can add more air up to about 72º
after that you will need expensive microbe additives to prevent root rot.
Solution temps above 78º are almost impossible to successfully grow dwc in,
even with the expensive microbes.
Saliniity is a big factor
in how much DO a solution can absorb.
Without high DO you will get disease.
Dissolved Oxygen(DO) is the only way to prevent root rot.
Anaerobic solutions will always become diseased.
If you are using 100% nute loads,
you are diminishing the ability of your solution to hold DO.
The higher your rez temp is,
the more important it is to reduce nute loads.
Check your roots
and if they are slimey
flush out the nutes
and run a hydrogen peroxide solution
for a couple of days.
Then flush that,
and add some emzymes for a couple of days,
to let the enzymes eat the dead roots.
Then leave the enzymes in,
and add your nutes,
at a 50% nute load,
and keep the solution temp lower.
.
Peace
