I emailed AN with the same pictures and this was there respond… Not sure if I agree with what they think it is or the temp range they suggested. I’ve always read 72 degrees max.
I keep it 72 and below
Thank you for your email.
The roots shown appear to have the onset of pythium beginning.
This is likely due to the water temperature. Ideally it should be kept at 66-68°F as temperatures of 70°F and above are a breeding ground for root rot/pythium and other pathogens.
In regards to supplementing with cal/mag the base nutrients will have enough for your grow’s purposes with RO water.
To resolve your root issue;
Drain entire reservoir, take pH water of 5.5-5.7 pour on top of medium at top of plants where they go into rockwool etc. drain that out too.
Wipe down reservoir, fill with water.
Add 15mL or 3 tsp of 28% hydrogen peroxide for every 1 gallon of water.
Run that through system. Take one jug of water out of reservoir and apply to each plant directly at root zone, let that run for two hours.
After two hours dump bucket out, run pH water through top of plant/container and dump it out, fill up with water, replace with nutrients and all root rot should be dead.
The brown will still be there but the slime should be gone from the root zone.
After three days, open the bucket up and take a look and you should see bright white new roots starting to grow.
Then ensure temperatures are kept at 66-68°F in best efforts to avoid running in to this situation again.
Please let us know if you have any further questions.