How Long Can Koi Live Without Oxygen? Guide to Koi Oxygen Levels
Most fish require at least 6 parts per million (ppm) of dissolved oxygen – once levels fall below this level, fish become stressed and may have reduced appetite, won’t spawn, and will likely be lethargic.
If oxygen falls below 3 ppm, fish begin to suffocate and die. 8 ppm or above is recommended for most fish, including koi, though they will survive so long as levels don’t fall below 6 ppm. If oxygen levels are consistently low for an extended period of time, fish growth can be stunted or even deformed, and fish become more susceptible to illness and disease.
Low oxygen will also have an adverse affect on water quality, as denitrifying (beneficial) bacteria require high levels of oxygen to efficiently break down harmful organic waste compounds, such as ammonia and nitrites.
What Influences Koi Pond Oxygen Levels?
The particular length of time that koi can survive without adequate dissolved oxygen depends on a variety of factors, including the exact level of oxygen present as well water temperature, water movement, salinity, and many others.
As a general rule, warmer water holds less dissolved oxygen than cold water. This is because cold water is denser with water molecules that are packed more closely together, thereby making it more difficult for oxygen molecules to escape the water. Water that is above approximately 85° F (29°C), again depending on a variety of other factors, can only hold approximately 6 to 7 ppm of oxygen, whereas water that is 70° F (21°C) can hold 8 to 9 ppm of oxygen – essentially, temperature is a massive influence!
Furthermore, water that is moving has more surface area than still water, thus increasing the likelihood of holding more oxygen. This is particularly true if the water is somehow splashing or moving over something like a rock, whereby the water picks up oxygen molecules from the air and carries them back down into the water. Elevation also plays a role – if you’re located at a higher altitude, there is less air pressure and therefore less oxygen in water because there is less force essentially pressing/holding the oxygen in the water.
How Long Can Koi Survive Without Oxygen?
With all of the above in mind, the amount of time that koi can survive without an active oxygen supply can range from a couple of hours to several days. If there is no dissolved oxygen present in the water, then obviously they will die in a matter of minutes. So long as there is already at least 5 to 6 ppm of dissolved oxygen in the water, they should be alright for at least a couple of hours until you can incorporate at least one (preferably several) of the solutions covered below.
Long-term Koi Pond Oxygenation Methods
Any fish pond truly needs an air compressor to provide oxygen continually and long-term. Air compressors utilize an on-land unit with tubing that transports air to an underwater diffusion plate in another portion of the pond (usually the bottom), where it then rises as air bubbles that distribute throughout the pond. Air compressors are powerful, and therefore well suited for larger ponds and/or those that are heavily stocked with fish and consequently need a more rigorous oxygen supply.
As mentioned above, water movement also increases oxygen supply both by boosting the water’s surface area and also by trapping air molecules in the water as it moves. Fountains, waterfalls, or even having a tiny stream flow into your pond are all great ways to consistently add some oxygen to your pond.
Discussed in many of our other articles, incorporating plants in your pond is a fantastic natural way to both add dissolved oxygen and also filter the water of excess nutrients and any pollutants that may be present. They also provide shelter and habitat for your fish and any other residents like turtles and frogs, and a potential food source for them as well. Though submerged plants are the best at adding oxygen directly to the water, having a mixture of native submerged, floating, marginal, and bog plants is best for overall water quality as well as the health and happiness of your fish and the ecosystem.
Shading your pond is also a good way to help protect oxygen levels in your pond. You shouldn’t shade all of your pond; rather, strive to shade only a portion of it, ideally 40% or less, so that there’s still enough sunlight for plants, any reptiles and amphibians present, and various microorganisms. The shaded portion of your pond will be cooler, and therefore will be better able to hold more oxygen. Circulating the water will help move this oxygen to other portions of the pond. With similar logic, you can also perform water changes to incorporate clean, fresh, cooler water that can hold more oxygen. You can change up to 20% of the water out per week – less than this is fine, though certainly not more (unless there are water quality issues) as it can shock your fish.
Short-term Koi Pond Oxygenation Methods
In some cases, you may need a quick supply of oxygen – power outages, transporting fish, or an air pump breaking down are all instances in which you may need to use one of these methods. Keep in mind, though, that these are intended only as a short-term solution, as long-term they will not provide adequate oxygen and some could be harmful for fish if used for extended periods.
If you’re transporting koi in stock tanks or quarantine tanks, ideally they’ll only be there long enough to get to their next location or to recover from some form of injury or illness. Therefore, simply performing regular water changes in addition to adding a small bubbler (air pump) or even just a household fan blowing on the water can help mix oxygen into the water. Basically, the more surface disturbance you can create, the more oxygen molecules will be able to dissolve into the water. Since these methods are only designed as temporary solutions, not to replace air compressors or large aerators, you can get creative with methods so long they don’t provide too much stress on the fish.
Either in temporary tanks or in your pond, oxygen tablets can also be utilized. However, as covered more in-depth in our article on oxygen tablets, these should only be used as a last resort. They contain hydrogen peroxide and various sodium compounds that dissolve in water and create bubbles. These compounds can, of course, adversely impact water quality, may burn fish scales and gills, bleach fish eggs, bleach plants, and possibly kill off beneficial bacteria in the water. The exact dosage and concentration is highly contested, as the point at which these tablets can become toxic depends on existing water quality parameters as well as the fish species that are present.
Further Tips & Tricks to Avoid Oxygen Deprivation In Koi Ponds
In addition to the main methods above, there are a few other things you can do that, while they won’t themselves incorporate more oxygen into the water, they will reduce oxygen depletion. Try to really limit your use of fertilizers and any chemicals, such as herbicides, near your pond as these can runoff into your pond and damage water quality parameters such as pH, which can in turn mess with dissolved oxygen concentration. Fertilizers in particular will help fuel the growth of potentially harmful algae and bacteria, which will deplete oxygen. By the same logic, if you cut your grass do so at least a meter away from your pond and keep the clippings away from and out of your pond.
If you have pets, whether they’re dogs, goats, cats, or horses, do keep them away from your pond. They can trample emergent plants in and around your pond that help add oxygen to the water and filter it, increase erosion and sedimentation in your pond, and could also defecate in or near the water, which will add nutrients to the pond and deplete oxygen levels in addition to diminishing overall water quality.
Also do your best to not feed your koi more than they need, giving them only as much as they can eat within 5 minutes and making sure that you clean out any uneaten food. Food that is left in the water will add nutrients to the pond and, again, use up oxygen as it breaks down while also adding nutrients to the water that will feed algae. Also, feeding a high quality food with ingredients koi can actually use will ensure there is less waste excreted into the pond in comparison to low quality foods packed with “filler” content.