koi invierno

How to prepare my koi pond for winter

Better late than never.

I honestly have to admit that I had not thought to write anything about winter.

In Koi Hacienda the minimum temperature – of the water – is 15 degrees, due to being located near the Mediterranean coast and having semi-covered facilities (see virtual tour to understand better).


alimentacion koi

Big pond in Koi Hacienda

But telephone calls, emails and WhatsApp – really startling – of some customers have made me see that the winter in other areas of Spain is a very delicate period for the koi:

  • How to prepare my koi pond for winter?
  • Should I break the ice?
  • My koi lying on the bottom of the pond
  • Can I introduce new koi if my water is 2 degrees?
  • Should I give another type of feed in winter?

These and many more questions have come to me the last few weeks and are answered in this article “how to prepare my koi pond for winter”.

First of all I would like to make one thing very clear: Koi are cold-blooded fish. What is a cold-blooded animal? It is an animal whose own organism does not produce a body temperature. Therefore the temperature of the body is practically the same as its environment (in the case of the fish with 0.5º of difference).

A koi can survive for two months at 2 ° C if it has enough oxygen.

At these temperatures the metabolism of the koi is working very low. Any stress (removing the koi, changing the site, raising the water temperature by more than 5 ° in a day, etc.) can lead to shock, heart attack, even death.

How to prepare my koi pond for winter? 

Here are 8 aspects to take into consideration: 

1. Health

So that the koi can pass the winter without stress, it is important that they enter healthy in the cold season. If the koi are already “groggy”, it will be very difficult for them to endure a hard winter.

How to make koi well prepared? Especially the parameters of the water have to be correct.

If that is controlled, we can help to increase the koi’s own defenses with a Malamix cure. It is an absolutely natural product with ingredients such as aloe vera, marigold, ginger etc. Developed by veterinarian Maarten Lammens specialist in koi (see product sheet Malamix17). At Koi Hacienda we have many fantastic experiences with this product and highly recommend it.



2. Feed

If temperatures drop, we must adjust the type of feed.

While we, the humans, like the strong food in winter and light in summer, for the koi is just the opposite: Very nutritious in summer because it is their time of much activity and pre-digested in winter because their organism slows down until hibernation.

As a general rule you can say:

  • More than 20 ° water temperature: special feed for the development of colors (eg Ichi Excellent)
  • Between 15º and 20º water temperature: summer feed (eg Ichi Summer)
  • Below 15 ° water temperature: winter feed (eg Ichi Winter)
  • Below 10º water temperature: DO NOT FEED

Those who want to strengthen the own koi defenses, can mix the feed of each period with the Malamix feed. So we are doing here in Koi Hacienda and the truth is, it gives us very good results.

alimentacion koi

If temperatures drop, adjust type of feed


3. Depth

In most articles I indicate the importance of pond construction. I am aware that I repeat myself, but this is the basis of the well-being of the koi. Same as building a house: if there is botch in the basement, on the 5th floor we will encounter serious problems.

We insist on a wise construction of the new habitat for your koi and above all a dignified depth: minimum 1,50m. If it can be more, better (in Koi Hacienda the big pond is in the deepest part 2.70m). Depth is not only required so that koi can develop their torpedo body shape, but also because of temperature: in summer, down there is less heat. In winter, down there it is less cold.

Depending on the area, the soil, the insolation etc. as a rule it can be said that at 1.50m from the surface, there is still at least 2ºC.


4. Oxygen

Low temperatures are one aspect, but frost on the pond surface is another aspect. While koi can withstand temperatures up to 2 ° C (should not last longer than 2 months), it is absolutely essential that they have oxygen.

Oxygen is a complicated phenomenon elevated to two:

A) the warmer the water, the less oxygen itself carries

B) the warmer the water, the more active the koi, the more oxygen they need

In winter, the situation is obviously reversed: cold water contains more oxygen and koi need less because they are less active. They need less oxygen, but they need oxygen.


4.1. Oxygen through a waterfall

Let’s not fool ourselves: A waterfall is more a decorative object than an essential part of the installation of a koi pond. In summer usually it does not bring enough oxygen and in winter it scares the koi if it is not turned on continuously.

koi en invierno

Waterfall impeding freezing the pond


4.2. Oxygen through an external pump

An installed air pump that pumps oxygen into the pond is the most sensible option since this same pump can also be used in summer when the koi need more oxygen. Depending on the depth of the pond, a more or less powerful pump is required. It is important to take into account the electric consumption of that pump since it will work many hours. Due to this fact (constant operation) it is important to choose a silent pump. We in Koi Hacienda use with full satisfaction models of the Alita brand.


4.3. Obstacle

To prevent the entire surface of the koi pond from freezing completely, special objects have been developed as you can see in the picture. It has to be a floating and insulating object, so that the water does not freeze inside the obstacle.

estanque koi invierno

How to prepare my koi pond for winter ? (fish hole of www.tovie.com)


5. Never

I write it as a separate point, although it should be included in the previous topic. But as it is of vital importance, I give it its own title:

Never break the ice in the pond.

If during the summer, a child throws a stone at the pond, it is nothing serious (although undesirable). But if in winter, when the koi have slowed their metabolism so much, every abrupt action can cause so much stress that the koi goes into shock and dies. I’m not exaggerating at all. The most dangerous: this shock may come to light days later and then many people do not associate it with what happened.

In order to open the surface, take some boiling hot water and let it run onto the surface, melting it until you have a hole. Use then an obstacle, so that the surface can’t freeze completely again. 


6. Heating up

There are many koi lovers who are warming up their ponds in winter. Apart from being a great investment in machines, it also represents a great expense of electricity. This “solution” obviously means less stress for the koi, but on the other hand it also entails disadvantages. As previously stated, the koi is able to live in water up to 2°C (for a limited time). If nature predicts so, why does humans have to oppose? The cold season is essential because it gives the koi rest. This rest is essential for the growth of the koi (koi kept in constantly warm waters will not be larger than those experiencing hot and cold times). It is also said that constant high temperatures increase the risk of accumulation of eggs, tumors and other disorders of metabolism.

If a owner opts for this remedy, the best would be a temperature of 8°C for two months. As spring approaches, you should adjust the temperature gradually (maximum 4° per week) to 14°C.


7. Cover

Covering the pond can be another option to protect koi from low temperatures. Depending on the size of the pond, there are different ways. A special construction of wood, some canvases, branches, reeds … there are many ways and many materials. The important thing is that it can enter light (UV) and oxygen.


8. Quarantine pond

Like humans, there are koi who can withstand the cold and others less. For those fish that are more delicate, a solution to protect them from cold is to mount a quarantine pond in a protected area such as a garage, a workshop … This option requires space and a complete equipment for the quarantine pond and with filters, pumps etc. as the equipment for the main pond should continue to work there. 

Attention: Never leave the quarantine pond outside. If it does not have any protection, the whole water volume could freeze (including the koi).


How to prepare my koi pond for winter is an entry of the blog.

It is open to comments and suggestions.

Thanks for sharing.