Hi
@Stooooned! Hard to say without any pictures but it sounds like root-rot. Are you sure your air-pump is still 100% working? Are you sure there's absolutely no light coming through your reservoir? How often do you fully change the solution in your reservoir? As an emergency move, you can prune the brown roots, keep the most healthy parts, and see how it goes. Take some closeup pictures so we'll be able to refine the diagnosis and help you to adjust your parameters. Happy growing 👊