Oxygen is measured in mg/liter or ppm. They are equivalent measurements so you can use either ppm or mg/l.
Every body of water has a maximum amount of oxygen which it can hold. This ability to hold oxygen is dependent on the temperature of the water, the atmospheric pressure and to a lesser extent, salinity.
- Cold water can hold more oxygen than warm water.
- Low elevations can hold more oxygen than high elevations.
- Fresh water can hold more oxygen than salt water.
The maximum amount of oxygen a given body of water can hold is called its saturation point. Our goal is to try to maintain oxygen levels as close to saturation as possible. This is not easily done.
Many factors influence the oxygen demand of the pond. Fish load, waste levels, bacteria count, algae production, etc all remove oxygen even as we are trying to replace it. Fortunately, the animal life in our ponds and lakes do not require 100% saturation of O2. However, there are certain safe levels or “percent saturation” levels where life can flourish. Generally, above 80% saturation is acceptable and more easily maintained. 80% saturation still gives us a margin of safety in case of a higher oxygen demand due to overfeeding or inadequate filter maintenance for example.
The graph below shows the saturation point of various waters in relation to temperature and pressure. Try to maintain your oxygen above 80% of saturation point.
For example, at sea level in fresh water and a water temperature of 75 degrees 100% saturation is 8.4 mg/l. 8.4 x 80% equals 6.7 mg/l. Ponds or lakes maintained at higher levels will function better and handle higher fish loads with less disease and better growth rates. There is a higher safety margin.
If your existing system cannot maintain oxygen above 80%, you should incorporate a HAKKO air pump to increase aeration and maintain your filter system more regularly to reduce waste levels.
Oxygen Saturation Point Chart
|Temperature||Fresh Water mg/l||Saltwater mg/l
|°F||°C||Sea Level||2,000ft.||Salinity @
35ppt sea water
|(mg/l = Milligrams per liter) (ppm=Parts per million)
(ppt=Parts per thousand salinity)
Basically, temperature has the most significant effect on oxygen saturation. Adequate aeration in winter temperatures may be totally inadequate in summer temperatures with the higher oxygen demand due to heavier feeding.
Elevation has a smaller effect on oxygen solubility and is a factor for consideration if you live in the mountains or high altitudes.
Salinity has a very small impact on oxygen saturation at the levels we keep in Koi ponds, generally only 5ppt or 0.5%. The benefits of salt for fish health outweigh the loss of O2 solubility.
It should be very obvious that it is difficult to over-aerate a pond. In fact, most ponds and lakes are inadequately aerated as revealed by ongoing fish health problems and excessive algae growth.
HAKKO air pumps can help make your water “alive” again.