If you want to add carbon dioxide to the fish tank, you can equip it with a carbon dioxide cylinder. Usually, fish farming does not need to add carbon dioxide. When fish breathe, carbon dioxide will be discharged. Only straw cans are needed, because aquatic plants need photosynthesis, and photosynthesis cannot be separated from carbon dioxide. Fish farming needs an oxygen pump to ensure its breathing, especially in the case of high feeding density. Lack of oxygen will lead to the death of fish.