Koi Staying at Top of Pond

koi fish with barbels

Koi Breathing at Surface of Pond (Gasping for Air)

If your koi stays at the top of your pond, it is usually a sign of stress. However, there could be a couple of reasons why.


Your pond or tank may not have enough oxygen to support the koi fish. If this happens, the koi will stay on top of your water, their mouths opening and closing above the water surface, looking like they are gasping for air. This behavior is commonly called “hurting,” but it may also be known as “piping” or other terms.

They are trying to relieve stress by consuming oxygen in the air. 

It is essential to reduce what is depleting or increase the oxygen level as soon as your fish starts displaying signals. Your priority should be to increase the oxygen level as quickly as possible.

Add an airstone or bubbler as soon as possible to aerate your water and increase oxygen levels. Spreading fish to another tank or pond will also help, but this is not the best solution.


Your oxygen levels may be sufficient, but your koi might not get enough oxygen through their gills or bloodstream. Fluke infestations on the gills cause this and make a koi fish come up for air.

Flukes can cause fish to lose their gills’ ability to function correctly. Praziquantel is an active ingredient in many medications. These medications can be used to treat flukes if they are administered correctly.


Sometimes, during high rainfall, your pond water’s pH can drop. Causing stress on the fish. 

This can be fixed by doing some partial water changes (around 30%) and giving it some time to recover. Just be sure not to use city water that contains chlorine. That will need to be dechlorinated before use. 


Another reason koi stay at the top of a pond gasping for air is Brown Blood disease

The cause is high levels of nitrite found in pond water, at an abnormally high level.

Nitrite is a product of ammonia reduction in bacteria and can enter the fish’s circulatory system through the gills. The presence of nitrite at high levels can lead to dark brownish-colored fish blood. This is why the term “brown blood” was given. Nitrite can chemically oxidize hemoglobin within fish red blood cells and transform it into another compound called methemoglobin. Methemoglobin doesn’t transport oxygen in the same way as normal hemoglobin. As a result, the affected fish can show low oxygen stress, even with saturated oxygen. Because their blood can’t absorb oxygen, the fish start suffocating. The stress does not necessarily kill the fish. Still, they can be affected the same way as fish exposed to classical low dissolved oxygen levels.

The color of the blood can indicate the severity of the condition. For example, reddish-brown blood is mild, while more severe cases have chocolate brown blood. The amount of hemoglobin found in fish blood is converted into methemoglobin, and the water’s dissolved oxygen will determine whether fish survive. Fish moderately affected by nitrite poisoning should stay in a water body with a dissolved level of 7 ppm. However, the same fish will likely die if placed in a water body with a group of 2.0 ppm.

Nitrite, an intermediate fish waste compound, is formed by ammonia being broken down by bacteria. Certain bacteria species eat ammonia. Ammonia-decomposing bacteria produce a waste product called nitrite. Other bacteria also use nitrite to make nitrate, which they then decompose. Nitrate is a compound that isn’t toxic to fish in concentrations typical in ponds.

Although most problems with elevated nitrite levels are experienced in the cooler months, they can also occur anytime. Sometimes, a similar but more rapid nitrite buildup can occur when ammonia builds up in cooler temperatures due to reduced phytoplankton activity and bacterial activity.

Ammonia-consuming bacteria produce nitrite faster than bacteria that convert nitrite into non-toxic nitrate in cold water. This situation can lead to nitrite poisoning if nitrite levels are significantly elevated. Cool water with elevated ammonia levels can lead to lethal concentrations within 24 hours.

Salt (NaCl) is the solution as an amendment to water. The chloride (Cl) is the part of salt that can prevent and affect the treatment of nitrite poisoning- typically found in typical salt. At the fish gill surfaces, the chloride competes for nitrite’s absorption. When water has a 9:1 ratio of chloride to nitrite, it absorbs the chloride ions more effectively than the nitrite molecules. This prevents nitrite poisoning and “brown blood” diseases.

You also want to keep organic debris like leaves out of the pond to keep tannins down if you continue to see koi breathing at the surface. 

Do some water changes, and increase biological filtration.

Last Updated on August 1, 2022 by Davin