my plants have been getting root rot

[farm]

Hi Ron, I have a system where my plants are in Rockwool and are sitting in an aerated nutrient solution 24/7. This has worked fine for me in the past, but recently my plants have been getting root rot and dying. I'm wondering what the lowest temperature the water could be before the roots start dying. If you have any other suggestions as to why this is happening please let me know. Thanks, your sight has been a great resource.