Koi Pond Water Temperature Changes. Winter Summer Pond Temperatures

There's not much we can do to control the effect of extreme weather changes on the water in koi ponds. But this needn't be too much of a cause for concern since koi quickly acclimatize and adapt. Similarly goldfish and other pond fish will also usually adjust to pond temperature changes without any ill effect.

Pond temperatures versus air temperature

In general air temperature changes are more radical than the changes in water temperature in koi and goldfish ponds. This is quite simply because water heats up more slowly than air does. The same applies to the time water takes to cool. So while changing weather conditions may result in rapid changes in air temperature, the pond water becomes a kind of buffer for the koi. Furthermore, the deeper the pond, the more constant the water temperature will tend to be. Also, as the water gets colder and loses density prior to freezing, the icy water rises, encouraging koi to move to the warmer depths of the pond.

If you are new to koi keeping, do yourself a favour and buy a pond thermometer to monitor the ongoing shifts in the water temperature. You may be surprised at how little the pond temperature actually changes (particularly in areas where ponds don't freeze in winter). Not only will this help to keep your mind at ease, but it will also put you in a position of being able to make an educated decision in terms of whether to cut down the food you are giving your koi. At the same time, your koi will let you know whether or not they want food, and you really do need to pay attention to their needs.

In winter koi go into hibernation, and they don't eat. Once the water has dropped below 4 degrees C, they will stay near the bottom of the pool, where the water is warmer. They won't be looking for food. A good rule of thumb to remember is that they won't be actively looking for food until the water temperature rises above 8 to 10 degrees C.

The effect of rapid shifts in temperature

Like all creatures that go into hibernation, koi are driven into hibernation by a radical change in temperature in their environment. So, when what has been relatively warm water becomes cold water, your koi will tend to stop feeding and move to the bottom of the pond. Even when ponds don't ice over in winter, this is typical fishy behaviour. If this is caused by an unseasonal cold snap, chances are the koi will become relatively active again when the weather clears.

The only way to minimize rapid pond temperature swings is to install a pond heater that is thermostatically controlled. This way you can maintain a temperature of say 10 degrees C from late autumn to early spring. But remember that it is perfectly natural for koi to stop feeding through winter.

How water temperature affects feeding

It is a fact of koi life that in cold weather (and therefore in cold water) these fish need less oxygen and less food to survive than when they are active in warm water. When they are active, they need more food and are able to absorb and digest it. When they are inactive, they don't digest the food adequately which leads to an increase in fish excreta in the water. If you don't have a reliable filtration system, this can be a much bigger problem than radical swings in pond temperature – because it affects the quality of the water. If anything is going to adversely affect koi it is poor water quality. In fact if you aren't going to install a filtration system, you'll be better off keeping goldfish than koi.

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