She died. Not going to say I am surprised, but it still is sad. Picked up some tetracycline today, just dosed the main tank, moved my snails to a different tank. Gorgon still seems like her usual self. Hecate, however, was very pale, though I saw no fungus on her eyes or any part of her body.
In retrospect, I should have done a water change before I treated the tank.