Sometimes the information we receive from friends, club members and, yes, even dealers can be less than accurate. For some reason, in this hobby, old or outdated information and sometimes outright myths are perpetuated without much thought given to the current validity of the information. Often, people don’t seem to question the information they are given but, rather, simply accept it as fact.
If you have a waterfall you will have all the air your pond needs!
Myth or truth?
The truth is, even with a good waterfall, you may not have enough air (oxygen) in your pond to accomplish all the things that are happening in your pond that require oxygen.
1. Your fish require large amounts of oxygen to support their activity and growth.
2. Your filter requires large amounts of oxygen to support beneficial bacteria growth and the nitrification process.
3. Through a process known as photosynthesis, all the plants, including algae, in your pond will use oxygen during periods of low light and darkness.
4. The warmer the water the less oxygen is available for the above process to function.
For this reason just about every pond can benefit from, and should use, supplemental aeration.
Low oxygen levels will adversely affect fish growth rate and their ability to fight illness and disease. It will also have a dramatic effect on water quality. Understand, only water that makes actual contact with the air will absorb oxygen. In many cases, the amount of water surface to contact the air in your waterfall and stream may be pretty small. Not all of the water going over your waterfall or stream is oxygenated. Only the surfaces that actually contact the atmosphere. Your waterfall may not oxygenate the water to full oxygen saturation level.
1. The maximum amount of dissolved oxygen in water is called its saturation level. Saturation levels decrease as the temperature of the water increases. For example,
at 70 degrees, water saturates at 8.9 parts per million (ppm). At 80 degrees, saturation is achieved at 8.0 ppm, and at 90 degrees only 7.3 ppm. At higher temperatures, fish etabolism also increases and they use oxygen faster. Therefore, at 80 degrees, oxygen concentrations below 5.0 ppm may quickly prove fatal.
2. The oxygen required to oxidize one gram of ammonia to nitrate is 4.18 grams. If it is assumed that 1 pound of feed generates 14.6 grams of total ammonia nitrogen (TAN), then 1 pound of feed requires 61 grams of oxygen for the nitrification process just in the biological filter.
3. At 74 degrees water temperature a fish weighing one pound requires approximately .13 grams of oxygen per hour or 3.2 grams per day.
The pond is 3000 gallons and contains 10 twelve inch koi. A 12 inch koi weighs roughly 1 pound so we have ten pounds of koi in the system. Koi should be fed one tenth of their body weight per day. This equals one pound of food. One pound of food produces roughly 14 grams of TAN. 61 grams of oxygen are required for the biofilter to convert. Ten, one pound koi need approximately 32 grams of oxygen. So, doing the math (and I hope I did it right) we would have a demand of approximately 8.1 ppm (parts per million). Saturation level is only about 9 ppm at 74 degrees. That leaves less than 1 ppm and does not take into consideration additional oxygen demands from other biologic functions. The next morning you may find some of your fish did not live through the night. If your waterfall is not oxygenating the water to the saturation point you might not have sufficient oxygen to the filter, which means nitrifying bacteria will die and water quality will diminish. In addition your fish may begin to die as well. Adding an air diffuser and pump to the pond will help with fish health, growth and water quality. It will also help gas off any toxic gasses from the pond AND CO2. CO2, Produced by oxygen consumption, will convert to Carbonic acid which will cause PH to drop if not gassed Off.