Koi Pond Water Temperature

Koi Fish and garden ponds are naturally heated up by the sun. Ponds with large volumes of water and/or deep water will take longer to heat up. Furthermore, water requires a lot of energy to heat it up so it will take many days of hot sun before a pond’s temperature warms up. Conversely, the pond will keep its temperature for several weeks after the first cold snap of autumn. Koi Fish , like all fish, cannot control their body temperature, so whatever the water temperature is will be the temperature of fish, too.




Koi are naturally warm-water fish and, in the UK, they are on the edge of their tolerable conditions. Unsurprisingly, they visibly respond to warm water and all their natural processes are geared to temperatures around 18–22°C (such as breeding, digestion and growth). Koi are much more active and responsive when it’s warm, leading many people to artificially heat their ponds.

High temperatures are not without their problems, though. Warm water holds less oxygen than cold water (see the Dissolved oxygen section), but because all the processes in a Koi are going faster when the fish is warm, its need for oxygen is greater. Therefore, in warm water, Koi can have oxygen shortages and might come to the top of the pond (where there is relatively more oxygen) to breathe. Also, in warm water some pollutants (see the Ammonia, nitrite and nitrate section) are more toxic and more likely to poison fish.

Cold water, of course, will contain more oxygen and some toxins are less harmful, but Koi will naturally slow down as it gets colder. Below 10°C, a Koi’s systems are on ‘tick over’. It will not digest particularly well so it feeds less. Its immune system, which protects a Koi against disease-causing organisms, is very limited in cold water so outbreaks can occur.

Heating a pond does keep fish more active for the whole of the year. It also means they grow all-year round. On the other hand, it is expensive and it is not an environmentally sound practice. If you do decide to heat your pond, make sure the fish have a cool period for a month or so in the winter because this lets a Koi’s body clock set itself to the natural seasons.


Source:
http://www.koimag.co.uk/advice/water-quality/koi-pond-water-temperature