The dissolved oxygen at the bottom and top of the biochemical pool is different. According to relevant public information, the dissolved oxygen content at the bottom of the biochemical tank will be lower than that at the top of the tank. This is because the flow of water and the diffusion of oxygen are affected by factors such as water depth and water velocity. The bottom water flow is slow, and it is easy to form a dead zone, resulting in low dissolved oxygen content, while the top water flow is fast, and oxygen molecules are easier to diffuse, so the dissolved oxygen content is relatively high. Biochemical pond is a kind of filter in aquarium. Through the interaction between biological filter media and plants, harmful substances in the aquarium are transformed into harmless substances, and at the same time, the oxygen content in the water is increased to maintain clean water quality and healthy growth of fish.