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Oxygen levels in a pond are very important to the overall health of the koi. It is important to realize that plants and algae produce oxygen during the day light hours, however, at night the whole process is reversed and plants and algae actually consume oxygen. This is important because sometimes people will turn off their pumps at night to conserve energy and wake up to a pond full of dead fish in the morning and have no idea what happened. We saw one case where a man had turned off his pump at night for two years and never had a problem and then during one hot summer night he lost them all without any warning. The problem was that the koi had continued to grow until they reached the critical point to where the oxygen in the pond, during the night, could no longer sustain them. The most common way to add oxygen to the pond is by use of a water fall or air bubbler. Anything that disrupts the pond surface will help add oxygen. The only place where oxygen can effectively be transferred into the pond water is at the pond surface where the atmospheric pressure on the water and the oxygen is equal. Placing an air stone in the bottom of a pond will not add any oxygen into the pond until the bubbles reach the surface and break. The major advantage of using an air stone at the bottom of the pond is that as the bubbles float to the surface they bring along with them the water from the bottom of the pond which is usually low in oxygen. This creates a constant current of water moving from the bottom of the pond, where the oxygen level is low, to the surface where it can pick up oxygen. The down side of air stones is that often times they end up causing the pond to look like a Jacuzzi, making it harder to see the koi because of all the bubbles on the pond surface. An alternative to air stones, that works well, is to use jets to move the water to the surface where it can be oxygenated. The advantage of using jets to move the water, instead of air, is they cause much less disruption on the pond surface. The only way to accurately test the oxygen level in water is to use a digital oxygen meter. Oxygen testers start at around $175.00, so for most people it is not practical to purchase one. Therefore, most people will have to guess as to how much oxygen their pond contains. As a rule, if the pond has an average sized waterfall and you can hear the water flowing you most likely have enough oxygen. On the other hand, if the koi spend most of the day near the water fall or are constantly near the surface of the pond you may need to increase the oxygen level. A pond with a consistently low level of oxygen can contribute greatly to koi fish that don't grow or that are often times sick. |
