The most important aspect of pond-keeping is ensuring your Koi are kept healthy and safe. There are plenty of things that can be detrimental to your Koi, but luckily, most are preventable. Below is a list of things that can kill your Koi and Butterfly Koi and tips for preventing a fatal outcome.


If you check on your Koi one morning and notice a few missing, predators are the likely culprit. The predators that may snoop around your pond depend on the region you live in, but herons and raccoons are common unwanted pond visitors.

Thankfully, there are plenty of ways to protect your pond from predators. The design of your pond can make a huge difference in protecting your Koi, Butterfly Koi, and Pond Goldfish. Deeper ponds make it more difficult for predators to reach fish. It’s also helpful to give your fish hiding places, including caves, footbridges, and plants. Covering your pond with netting can also prevent predators from getting hold of your Koi. Other deterrents include decoys and motion-sensor alarms and lights.


Unfortunately, a parasitic infection in Koi can be very difficult to catch early. But there are steps you can take to help prevent parasites from getting close to your fish. Parasites most commonly enter a pond via a Koi that is already infected, which is why the best way to prevent parasites is to properly quarantine all new fish before adding them to your pond. Koi can also contract parasites from contaminated water and infected food. Make sure your water is in the best shape possible. Store food in an airtight container, and don’t use it past the expiration date. If you notice any worms or insects in your fish food, get rid of it.

The signs, symptoms, and treatment for a parasitic infection depend on the type of parasite you’re dealing with. (The same goes for bacterial infections, which we’ll cover next.) Our Comprehensive Guide to Koi Diseases can offer some guidance.


Bacteria is always in your pond. However, assuming your pond is clean and your Koi are healthy, the bacteria present in your pond shouldn’t pose a threat to your pond ecosystem. Koi become susceptible to bacterial infections when they’re under stress or the immune system is weakened–which can be caused by parasitic infestations, predators, and poor water quality.

Bacterial infections are usually a secondary issue. For example, if a Koi has an open wound from a predator attack, it can easily contract a bacterial infection. The best way to prevent bacterial infections is to prevent the primary issue by keeping your Koi and Pond Goldfish safe and healthy and keeping your pond water healthy. Learn more about Aeromonas hydrophilia, a common pond water bacteria.

Poor Water Quality

Poor water quality is a common cause of Koi death and one that is preventable. First, it’s important to remember that just because the water looks clean doesn’t mean it is healthy. Crystal-clear water can still contain invisible toxins and pollutants that can cause illness and death. Poor water quality can be caused by a number of things, including debris, excess waste, poor filtration, and overcrowding. Koi will typically exhibit signs of stress when water parameters are off, which might include flashing, jumping, loss of appetite, lethargy, gasping for air, fin clamping, and color loss.

The simplest way to avoid poor water quality is by being a good pond keeper. Regularly test water, remove any waste or debris from your pond, and make sure all equipment is clean and working properly. Performing routine pond maintenance will help ensure that your pond water quality stays in the best possible condition.

Shallow Water

Shallow ponds can be dangerous for Koi and Goldfish for many reasons. First, shallow water makes it much easier for predators to spot and grab your fish. Koi also occasionally jump. In shallow water, it’s much more likely they will accidentally jump out of the pond entirely. Shallow ponds freeze much more quickly than deep ponds, which can be detrimental to Koi if you live in a colder climate. Because shallow ponds have less water volume, harmful chemicals build up much faster than in larger, deeper ponds–which can lead to poor water quality that can make your pond population more susceptible to illness and disease.

To avoid issues, it’s recommended that your pond be at least three feet deep. Other factors, including climate, pond shape, and the number of fish in your pond, also affect how deep your pond should be.

Lack of Oxygen

Like humans, Koi cannot survive without oxygen. Koi absorb dissolved oxygen molecules through their gills, which then enter the bloodstream to help support biochemical processes, including breathing, cell formation, and digestion. Oxygen is also needed to keep water quality in good condition. The beneficial bacteria in your pond need oxygen to survive and reduce ammonia and nitrite levels.

The most obvious sign that your pond may lack oxygen is if Koi are gasping for air at the pond’s surface. Excess algae and a foul-smelling pond can also indicate low oxygen levels. The easiest way to prevent low dissolved oxygen (DO) levels is to monitor DO levels frequently. Koi ponds should have a minimum DO measurement of 6 parts per million (PPM). You can measure levels with a dissolved oxygen meter or a dissolved oxygen test kit.

There are also several ways to add oxygen to your pond. Pond plants will convert carbon dioxide to oxygen. Adding a water feature, air pump, or air stone to your pond can also increase oxygen levels. The movement from water features and aeration devices encourages gas exchange, releasing toxic gases from the pond and adding oxygen.


Overfeeding and underfeeding your Koi and Butterfly Koi can be equally harmful for different reasons. Overfeeding can lead to excess waste in your pond, negatively impacting water quality, which can lead to stress, illness, or death. It can also cause damage to the kidneys and other internal organs. Underfeeding can result in malnourishment, rapid weight loss, stunted growth, and death.

The general rule of thumb for feeding is to avoid giving fish more than they can eat in five minutes. This will discourage overeating and prevent uneaten food from being left in your pond, which will help preserve your water quality. It’s also important to remember that the metabolism of Koi changes with the temperature, which means their nutritional needs also fluctuate with the seasons. Koi cannot properly digest food in cold temperatures, meaning overfeeding can be especially harmful in the fall and winter months. In the summer, Koi are more active and must be fed more frequently. Knowing when and what to feed koi at different temperatures can help you avoid over and under-feeding.

The good news is that Koi death is preventable as long as you’re taking the proper steps to keep your Koi, Butterfly Koi, and Pond Goldfish happy and healthy, which essentially means being an attentive pond keeper. If something seems off, it probably is. Trust your gut, and don’t be afraid to consult other pond keepers for help when needed.

Ready to add a few new additions to your pond? Shop our full selection of Koi and Goldfish today.

Leave a Reply

Your email address will not be published. Required fields are marked *