I'd say the roots look fine, a little discoloring is normal. Its the actual chunks of slime you need to look out for. The first couple years I grew DWC I added beneficial bacteria in the form of compost teas, then I decided to try running a sterile rez so I stopped using the teas and started adding H2O2 instead. I honestly couldn't tell a difference between the two methods in terms of the plants health and yield but with H2O2 the rez and root mass looks cleaner so that's what I decided to stick with.