It's hard to say what the sediment is actually from. I use great white and have not had this problem.
The fact that you started to have unhealthy roots in the first place, even though temps are under control, is probably a good indicator that your dissolved oxygen is too low.
A lot of people don't believe in using beneficials in DWC because they don't think you should need to culture bacteria or fungi in the root-zone and it might get out of balance, also the fungi won't really survive with too much water and no soil to grow on or in. Again, I have not had this problem, but I do use great white very sparingly and I do believe some of the fungi will populate the root mass in the media above the water line.
You might want to look into more, or different air stones. Aeration is not necessarily best only with super fine bubbles. A super fine bubble stone might be too restrictive and not be letting a very high volume of air through. Also a lot of dissolved oxygen comes from the water movement itself at the surface. So you really want all your water surface to be disrupted with tons of bubbles and water movement from the air rising rapidly through the water to the surface. The movement at the surface of the water with the air is as important as the bubbles themselves.
I say focus on the more air and more movement because a 17 watt air pump sounds like it should be enough for your tote. I'm assuming it is a basic DWC with the net pot suspended above the single reservoir, and you are not using a under current recirculating system, as you didn't mention it. Also a undercurrent system would certainly need a water pump to recirculate the water from the main reservoir to the DWC undercurrent container.
Hope this helps,