The present invention relates to a carbon dioxide supply apparatus for an aquarium, wherein the carbon dioxide supply apparatus is connected with a carbon dioxide tank by a hose to supply a small amount of carbon dioxide, thereby sterilizing the aquarium. The carbon dioxide supply apparatus comprises: a metal supply pipe of stainless steel which is connected with the hose to supply carbon dioxide to the aquarium and formed in a cylindrical shape, wherein the metal supply pipe has a plurality of curved surfaces such that the metal supply pipe is mounted on one surface of the aquarium a cylindrical-shaped coupling part which is expanded from one end of the inside of the metal supply pipe and performing coupling by a screw and a cylindrical-shape whetstone mount pipe which is coupled with an upper side of the coupling part, wherein a porous whetstone is mounted on the whetstone mount pipe to finely supply carbon dioxide above. The carbon dioxide supply apparatus can be never damaged even though it is used for a long time in the aquarium and can be safely used regardless of physical impact, by providing the metal supply pipe of stainless steel for supplying carbon dioxide to the aquarium, and the carbon dioxide supply apparatus can be safely used for a long time and the whetstone and the coupling part can be easily coupled with each other, by providing the cylindrical-shaped coupling part coupled with the whetstone mount pipe, on which the porous whetstone for supplying carbon dioxide is mounted. The carbon dioxide supply apparatus can be safely used by connecting an aquarium fixing part for fixing the metal supply pipe to the aquarium. The supplying efficiency of carbon dioxide can be improved by providing an anti-backflow valve for blocking the backflow of water in the aquarium. The components of the carbon dioxide supply apparatus can be conveniently coupled with each other by providing a hose coupling part for facilitating the attachment or detachment of the hose.CO
