This is grown by Hydroponics

Hey, I'm growing lettuces and basil on my dwc system and noticed that the plants roots are rather brown and look a bit slimy. Most of the roots are stuck together and are brown colored, the roots don't smell earthly or bad, and the roots don't seem to be easy to pull out. The plant and the leaves themselves don't have any visible sign of disease or deficiency. Question is is this root rot or simply nutrient stain? If it's root rot are they still savable?

My father is a fan of hydroponics and he started doing/experimemting on plant to grow using hydroponics technology