Oxygen levels in your pond are one of the most important things for the health of your Koi! Without enough oxygen in your Koi water your fish will die.
During the day plants and algae will produce oxygen but at night the whole process is reversed and plants and algae actually consume oxygen. Many people will turn off their pumps at night to conserve energy. Make sure you do not do this or you could wake up and find a pond full of dead fish in the morning.
One of the most common ways to add oxygen to a pond is by installing a waterfall. In fact, anything that disrupts the surface of the pond will help add oxygen.
The only place where oxygen can effectively be transferred into the pond water is at the surface. This is because, at the surface, atmospheric pressure on the water and the oxygen is equal. That is why putting an air stone in the bottom of a pond doesn't oxygenate the pond until the bubbles reach the surface and break.
A benefit of having an air stone at the bottom of the pond is that the bubbles rising to the surface bring along with them water from the bottom of the pond. This water is generally low in oxygen. Thus, there is a constant flow of water moving up from the bottom where the oxygen level is lower, to the surface where it picks up new oxygen.
If you would like an alternative to air stones you can use jets to move the water to the surface. An advantage of using jets to move the water rather than air is that they cause much less disruption on the surface of the pond, affording a better view of your beautiful Koi.
The only way to accurately test the oxygen level in your Koi water is by using a digital oxygen meter. Oxygen testers start at around $175.00. If this isn't in your budget you will have to guess as to how much oxygen your pond contains.
As a general rule, if the pond has an average sized waterfall and you can hear the water flowing you probably have enough oxygen. Of course if your Koi spend most of the day near the waterfall or near the surface of the pond you may need to increase the oxygen level.
A pond with consistently low levels of oxygen can dramatically slow your Koi's growth rate as well as causing many other health problems in your fish.
Typical Koi Responses To Different Oxygen Levels:
3 ppm Koi begin to die
5 ppm Koi barely survive
7 ppm Koi will live
8 ppm Koi will do well
11 ppm Koi do very well
As you can see, oxygen levels are of the utmost importance to the health of your fish. Make sure you take these simple steps to assure proper oxygen levels in your Koi water.