Dissolved oxygen (DO) comes from two main sources: the atmosphere and photosynthesis. Most aquatic organisms require DO to survive and it is important for chemical processes in aquatic environments. Dissolved oxygen probes work by measuring the amount of oxygen that diffuses across a permeable (or semi-permeable) membrane into a probe (sensor). Once oxygen is inside the sensor, a chemical reduction reaction occurs, producing an electrical signal. This signal is read by the DO probe and is displayed on a meter. Pokcenser provide two categories of dissolved oxygen sensors: optical and polarographic. DO sensor for fish farming is so important.