A killing apparatus (11) for controlling algal blooms and killing pathogens in a fish tank includes a first conductive mesh (30), a second conductive mesh (50), and a spacer (40) which is disposed between the first conductive mesh (30) and the second conductive mesh (50) and insulates the first conductive mesh and the second conductive mesh. Accordingly, in the fish tank, algal blooms are prevented and reduced, fish disease is prevented, and the growth of water plants is expedited.
