Water has much less oxygen than air. High quality water has 20,000 times less oxygen than our air. Parts per million and milligrams per liter are equal. One pound of oxygen dissolved in a total of one million pounds of water equals 1 ppm dissolved oxygen. Water temperature, atmospheric pressure and dissolved substances control the amount of oxygen water can hold.
Cold water can hold more oxygen than warm water.
Water at sea level can hold more oxygen than water at higher altitudes. Salts and other substances in water reduce the oxygen holding capacity of water. Of these factors, temperature is the most important. As the number of plants and animals in your pond increases, the dissolved oxygen use increases. Likewise, as the total weight of plants and animals in your pond increases, the dissolved oxygen use increases.