Monitoring the temperature of your Koi pond is essential.  We recommend that a thermometer be floated in the filter/converter system or tied to an easy access point at the edge of the pond. 

CAUTION: Small floating glass thermometers can be swallowed by Koi.

On most occasions temperature will be lowest in the morning just before sunrise and the highest at sunset.   Temperature is influenced by the amount of sun, the intensity of the sun the pond receives and other factors such as the wind speed during the day or night. Evaporation cools the water.   Generally speaking Koi should not be subject to more than a 3 - 5ºC sudden change in water temperature.   Always adjust the temperature gradually when moving Koi around.  An increase in temperature is tolerated better than a decrease in temperature.  Most ponds have a 1 - 3ºC variation in temperature in 24 hour cycle.   You will notice that Koi are more affected by a sudden lowering of water temperature than a sudden raising of water temperature.

Feeding fish versus Temperature:

In all cases, try to feed only what the fish will normally consume in about 10 minutes. Remove any uneaten food within an hour.