Does it smell funny? Like stagnant?
Are the roots breaking apart easily?
If everything's growing fine and you don't have these symptoms, then you probably will have nothing to worry about.
However - the fact you have a lot of slime in there tells me that your res temps maybe way too high and assuming your a proper DWC, that it's not draining 4 times a day back into the header tank to remix and redistribute. Again tho that would give you a stagnant smell.
I'll also say again that your res it
too high. Your pots need to be just off the surface- your roots will submerge themselves. Water and rockwool cubes make gunge!
Make sure you also wash any clay pebbles THOROUGHLY, before they go into your system. They put off a lot of dust which makes a funk in the water.
If you're using RDWC then I would suggest trying a different brand of nutrients and start singling out what it can and can't be.
Go with liquid nutes. Powders in your DWC are obviously causing problems here.
That's my take.
Understand that the real darkness of the water, and the staining on the walls of the Rez is plain and simple the color that the nutes immediately turn the water when added. Even to a gallon jug of water and then shaken. Just like how a packet of iced tea powder would react. I mean I would be more then willing to switch nutes... But the plants look fantastic, rate of growth is well, and there is no flaws in the leaves or new growths. The main concern is the root which is why I started this, a bit hard to believe the source of the problems is the nutes
