Root rot was discovered in one of the K2s and it spread to every plant.
Deconstructed the entire system, added reflective tape to the bottom of the reservoir (oops), cleaned everything with antimicrobial soap, then white vinegar, and finally a rinse with H2O2.
Re-assembled and performed daily water changes for 3 days in the mornings and added 125ml of H2O2 in the evening to kill off the bacteria.
Plants finally began to see recovery. Trimmed all dead matter from leaves and removed some entire fan leaves as necessary after not seeing improvement matching the rest of the plant.