Home - Koi Medication - Koi Parasites - Sick Koi Symptoms - Pond Water Quality
Site Links

Symptoms Finder

You'll get a picture of the koi/goldfish, you click on the koi fish where it's sick, or choose from several other behavioral options that your koi may be exhibiting.

What KoiCrisis Is For?

Outbound Links

Need Help Now?

We offer FREE personal help with your sick fish and/or pond water quality problem. Fill out our easy “Help Form” by Aqua Meds

Feeding Koi

What to feed?
What not to feed?
How much to feed?
What to look for in labels?

Aqua Meds®

Have questions about care of sick fish and/or pond water quality problems and how to treat them? We have the answers.

Fish Medicines

Learn about fish medicines, what they do, and where to get them.


If you have a koi, pond or fish problem, this site takes you through twenty easy questions and at the end you know what you need to fix in your pond to create restored Koi health.



Koi Pond Care

Koi Pond Water Oxygen

Pond Oxygen is obviously essential to koi health, but how much or how little? Two test kits are available, I would recommend owning one of them. There is another test kit that is in a little vial you break in the water to be tested and collect a blue sample and compare it to a chart.

Minimum levels of pond oxygen would be 5ppm. This level will permit koi to live a few days. Pond oxygen levels as low as 3ppm at least partially explain why your koi are dying like flies. Levels as low as 7 could, and should be improved with an air stone o r Venturi pump. Pond oxygen levels over 8 ppm are desirable, but 11 or better (up to 14 ppm) are glorious. Low pond oxygen in your koi pond water is an underestimated cause of koi losses, particularly because of its synergistic effects with other toxins like Ammonia.

Hypoxia is 'oxygen starvation'. Most koi ponds are usually well served with venturi returns or waterfalls, but poor koi pond maintenance, high stocking levels and unusual climatic conditions can lead to low dissolved oxygen (DO) koi pond water levels. Low DO is likely to occur in summer. As koi pond water becomes warmer it can progressively hold less oxygen: and the koi become more active, leading to a greater demand for oxygen; and the bacteria in your koi pond and filters need more to, as do submerged green plants including algae.

The role of submerged plants and algae in your koi pond should perhaps be clarified. During photosynthesis, submerged plants release oxygen into koi pond water, which is why they are often called oxygenating plants. However, they also respire at the same time, extracting oxygen from koi pond water and excreting carbon dioxide. During daytime they produce more oxygen than they consume, but at night, when photosynthesis ceases, respiration continues and they become net oxygen consumers.

Clearly, if the oxygen demand exceeds the oxygen supply then the pond dissolved oxygen levels will gradually decline and this presents a serious danger to the koi. Common causes of low DO, apart from high fish densities, are heavy feeding and a dirty koi pond or pond filter.

A lot of pond oxygen can be used in oxidising organic waste and, under certain conditions, this extra demand may be 'the straw that breaks the camel's back'.

Unfortunately, a pond dissolved oxygen problem often occurs in the early hours of the morning. when we are not there to see its direct effects on the fish, rather than during the day when submerged plants are releasing oxygen from photosynthesis.

Typical clinical signs of low pond DO are lethargy and a tendency for the koi to gasp at the pond water surface and congregate around water returns. Many of these signs are the same as for a gill problem so a test for DO has to be made to be conclusive. There are cheap DO test-kits available but it is important to follow the instructions carefully to avoid introducing oxygen into the water sample by agitation or by pouring water into the test phial. If low DO is the problem, i.e. DO is less than 5 to 6 ppm (mg/liter), then additional aeration will help - but it is essential to determine what caused the problem and to take remedial action.