reading the diary from 10 ml to a liter of sensi a+b if this is correct
@GrowingGrannie is right and if your EC is 1.69 you are overfeeding them
I use sensi and I give 5ml and not always because it's too much when the plant is already bigger
now you'll say, another one telling me it's the nutrients' fault.... but I have 2 plants in there...
the difference is that now I'll explain to you....
not all plants are the same, some love nutrients and others don't..
in your case, you might have a more delicate plant than the other
if you fertilize correctly, the one that eats more will have to settle, and if you give the right doses it shouldn't complain, on the contrary, if you overdo it one will thrive without particular problems while the other will have many issues..
also check that the water is well oxygenated...
I saw that you use b-52 and Ancient Earth Organic, I advise against using these 2 products in DWC because they are heavy and leave a lot of residues that could clog the air passage in the water
plus they are organic and they won't help you much.. even the color of the roots could be darker because of them.