For our system such as yours, you want to run the most basic salt-based nutrient line. I would recommend the
general hydroponics flora series Lucas formula. Google it. Then use pool shock to sterilize your system. When you remove the plant to soak it in sterile water, take the machine and scrub it out completely. Then scrub it out again. Then take all of your neoprene collars, the pump, and every other part of the AeroGarden, and scrub them all out twice. Do the best job you can. Take every single piece of the pump apart and scrub it. Then run bleach or a heavy dose of
hydrogen peroxide through the system for 12 hours. Then rinse. Rinse twice if using bleach, as that can leave a residue.
Don't return the plant to any hydro system that hasn't been thoroughly cleaned and sterilized. Otherwise whatever form of rot you have will come back almost immediately. Avoid any organic inputs in your system. Learn how to make hypochlorous acid with pool shock and run sterile for cheap. The gh Lucas formula works well in a system such as yours. It's cheap and easy. No
calmag required. And top off your rez water daily. Treat with pool shock every 3 days to maintain sterilization.
While your roots don't have a severe case of rot, they have reached a point of stagnation. And you should be able to smell a slight decay. Keeping roots healthy long term can be difficult and maintaining a sterile solution is very important. If you see or smell rot, always dump your res, scrub it, and refill with clean solution. Keeping air lines, stones, and every other fixture clean is also required. Even after doing all of this, that plant is hardly smokeable. But use these techniques next time for a much better result. And you should always start out in dirt. It's much more forgiving.
I don't have a lot of root pics, but here are healthy roots at day 13 of veg. By day 71 they are massive.
